The Wisconsin governor, who dropped out of the presidential race in September, is in high demand while Republican candidates descend on his home state for the fourth GOP debate.
Walker remains a prominent conservative figure in the GOP and one of the most broadly-known Republicans who isn't currently in the 2016 race. An endorsement from Walker could boost the campaigns of several GOP presidential candidates.
"This is not an endorsement of Governor Bush,” Walker Spokesperson Tom Evenson said. “The governor is just willing to meet with any presidential candidate to talk about the issues that matter to voters.”
Meanwhile, ABC News has learned that Walker will appear at a closed-press event in Milwaukee for Rubio, who has been attracting some of Walker's major donors. The Florida senator said last week that he had reached out to Walker to “touch base” before the debate, but said he has not asked for an endorsement.
Evenson said he has not had any conversations with Walker about a potential endorsement in the Republican primary race.
But Wisconsin -- and Walker's influence there -- is valuable in the primary and general election process. The Badger State is a significant delegate prize toward the end of the nomination battle, making it a helpful boost to candidates who plan to go all the way.
Since dropping out of the race about six weeks ago, Walker continued in his role as governor of Wisconsin, meeting with advisers and posing for photo ops with Hilda, the "2015 Cow of the Year." But Walker may also have his own future in mind. With strong executive experience in Wisconsin, he could be on a short list as vice president.
Walker sent an email to supporters last week asking for money to pay for campaign debt. "When God closes one door, another one opens," he wrote in the email. "While I don't know exactly what the future holds, trust me, we will continue leading the fight for big, bold, conservative change in Wisconsin and across America."
ABC News' Candace Smith, Jordyn Phelps, Ines DeLaCuetara and Michael Falcone contributed to this report.