Sabally is eligible for the draft, which will be held April 17, because she turns 22 during this calendar year.
"After this season, I'm going pro. I really want to just fulfill my childhood dream and play in the WNBA and play professionally in Europe," Sabally told ESPN in an exclusive interview. "... It was very hard, but it was also a decision that just came from the heart."
She also announced her intention to turn pro on social media Thursday.
The 6-foot-4 Sabally is expected to be a top-four lottery pick, along with Ducks senior guard Sabrina Ionescu, who is anticipated to be the No. 1 selection by the New York Liberty. The Dallas Wings have the No. 2 pick and are followed by the Indiana Fever and Atlanta Dream.
Another Oregon starter, senior forward Ruthy Hebard, is also expected to be selected in the first round.
Oregon has four games remaining in the regular season. Sabally said Thursday's announcement will allow her to focus on trying to help the Ducks win their first national championship.
"I really just wanted to get it behind me because so many people were just asking me [about it]," Sabally said. "It was kind of stressful. I feel like now I have my head free and I can practice with joy."
Sabally said her family's financial situation also factored into her decision to begin her professional career. She has six siblings, including younger sister Nyara, a 6-5 redshirt freshman at Oregon, and said she would relish the opportunity to "give a better lifestyle" to a family who helped her achieve her goals.
"My family is not that financially rich or in the middle class," said Sabally, who added that she would also send money to extended family in Gambia. "I feel like I can finally give back and make their lives a little bit easier, pay their rent for a nicer house, because we were all squished together.
"... Just provide a life for my little brothers where they maybe have more than one pair of shoes for a whole season."
Sabally was born in New York and then moved to Gambia with her family when she was 2. They settled in Berlin, Germany, when she was 7.
Many WNBA players have supplemented their incomes with higher salaries playing overseas, but Sabally said the league's salary structure under the new collective bargaining agreement announced just last month was appealing.
In the new deal, the base salaries for rookies selected in the first four picks is $68,000, and picks 5 through 8 get $65,250. The remaining first-round picks get $62,500 their first season. Rookie contracts are typically three-year deals with a fourth-year option, which for the highest-picked rookies (picks 1-4) would be $86,701. The salary for the league's highest-paid players went from $117,500 to $215,000.
The new CBA also includes other cash compensation increases and, for the first time, the average player compensation will be in the six figures.
Sabally is averaging 16.0 points, 7.4 rebounds and 2.5 assists for the Ducks, who are leading the Pac-12 at 13-1. They play Stanford, the second-place team in the league, on Big Monday (9 p.m. ET, ESPN2/ESPN App).
She said her teammates and the Oregon coaching staff have been supportive, especially head coach Kelly Graves.
"He was like, 'I'm super happy for you, and just know that we all love you and you have full support,'" Sabally said. "And I was just like, 'Phew.' I could finally breathe. That was just awesome."
Sabally was the Pac-12 Freshman of the Year for the 2017-18 season, when she averaged 10.7 points and 3.8 rebounds. Last season, she averaged 16.6 points and 6.2 rebounds as the Ducks advanced to the Final Four for the first time in program history, losing in the semifinals to eventual national champion Baylor.
She also has competed with the German national team.
Not many juniors have left early for the WNBA draft -- mostly because they haven't been eligible from an age standpoint.
Players who compete collegiately are eligible for the WNBA draft if they have graduated from a four-year college prior to draft day, or within a three-month period after, or if they turn at least 22 years old in the calendar year in which the draft is held. They also can be eligible if their original college class has graduated (for instance, if a player is a redshirt junior).
In the case of Sabally, she turns 22 in April. In recent years, players such as Notre Dame's Jewell Loyd (2015) and Jackie Young (2019) both were draft-eligible juniors because they turned 22 in the calendar year of the draft and opted to go early. Both were selected No. 1.
Tennessee's Candace Parker, the No. 1 pick in 2008, left after three seasons of college competition but had been in school for four years after having redshirted because of a knee injury.
Oregon is 24-2 this season, projected as a No. 1 seed in Charlie Creme's Bracketology and ranked third in this week's AP Top 25 poll. The Ducks have won 12 consecutive games, including the program's first win over UConn in which the Huskies suffered their worst loss in Gampel Pavilion.
Oregon's 93-86 upset of the U.S. national team in an exhibition game in Eugene on Nov. 9 first got Sabally thinking she might physically be ready for the next level. In that game, she shot 10-for-18 from the field and had 25 points and 6 rebounds.
She said she spoke with Team USA's Nneka Ogwumike and Skylar Diggins-Smith about playing professionally.
"I feel like the USA game was just such a spark," Sabally said. "After that game, it was just eye-opening that I'm able to play at that level. ... That game really showed me what I need to improve on but also that I'm kind of there."
Sabally's offensive versatility at her size should continue to be a big asset for her as a professional. She has made 167 3-pointers in her Ducks career and generally has been more comfortable as a faceup shooter and penetrator, but her repertoire is expanding.
"I think she's really diversified her game; she's added some post-up moves," Graves said. "She's become better off the dribble. Before she was more a straight-line driver to the basket, now she can create a little bit -- not just for herself, but others. That's the biggest area she is still working on."
Sabally was ready to do more work in the classroom, too, but says she will graduate this summer -- she always intended to get her degree in three years -- with a bachelor's degree in general social sciences, with a concentration in crime, law and society, as well as a minor in legal studies.
"If I wouldn't have graduated this summer, I wouldn't have left," said Sabally, who plans on going to law school in the future.
Sabally said the Oregon staff will allow her to participate in senior night festivities next weekend, when the Ducks close out the regular season with home games against Washington State and Washington.
She was hoping to play alongside her sister at Oregon, but Nyara has had to sit out the past two seasons because of knee injuries. Deciding to leave her Oregon family behind was hard, but leaving Nyara also weighed heavily. Sabally credits her mother, Heike Krone, for being supportive throughout the decision to leave Oregon early, but especially for helping Sabally realize the time spent with Nyara, whether during official games or not, was special.
"She was always putting an emphasis on I had the two best years with Nyara," Sabally said. "And I don't have to regret everything and be like, 'Oh, I never got to play with Nyara.' I should rather say, 'I got to experience Nyara for two years.' That's what she told me and that really helped me, because I was devastated when she couldn't play this year."
When asked how she hopes to be remembered by Oregon fans, Sabally didn't hesitate to answer.
"I hope they remember me as a part of something great, and as a part of the team that brought home the national championship for the first time," Sabally said. "I'm leaving a great Sabally behind me [Nyara], and she's going to do great things and she's going to carry our name strong. I hope they will see me in her as well, but don't compare her too hard. Because she will have her own journey too."