Koji Uehara unavailable Saturday

— -- NEW YORK -- The Red Sox plan to hold off until they watch Koji Uehara long toss Sunday before deciding whether to send the 39-year-old closer back to Boston for additional testing on the stiffness he reported in the back of his right shoulder.

"He's unavailable today," Red Sox manager John Farrell said prior to Saturday's game against the New York Yankees. "We haven't gotten to the point of any roster move with him. We're still gathering information. We'll look to put him through a little bit of a throwing program tomorrow. That's the next step."

Uehara reported feeling stiffness after playing long toss with teammate Junichi Tazawa before Friday's game.

Edward Mujica, who saved 37 games for the St. Louis Cardinals last season before being replaced by rookie Trevor Rosenthal in September, saved Boston's 4-2 win Friday over the Yankees and will be the team's closer in Uehara's absence, Farrell said.

"One of the main reasons we signed him in the offseason is history showed us the need for multiple guys who can close games out in the event of a situation [like the one] that arose last night," Farrell said, alluding to how Boston lost two closers, Joel Hanrahan and Andrew Bailey, to season-ending injuries in 2013. "[Mujica is] a guy who saved 30-plus games. He walks to the mound very comfortable and we've got complete confidence in him."

Uehara said after the game he could have pitched, but didn't want to risk aggravating the condition. He said he felt the stiffness in the same area he did while playing catch on June 10, 2012, when he was with the Texas Rangers. That injury was described as a strained latissimus dorsi, a muscle in his upper back, and he missed 66 games. After his return on Aug. 26, he made 17 appearances for the Rangers and posted a 1.23 ERA, striking out 21 and walking 1 in 14 2/3 innings.

"Any time you've got a pitcher unavailable, there's immediate concern," Farrell said. "We're also getting to know Koji. This is the first time we've had to deal with him being unavailable. We've got to respect how he reacts to the discomfort that's there, the tightness that's there.

"We also know when he was in Texas there was a setback during the time he was on the DL. So to say this is a direct comparison to two years ago is probably a little bit too early, but we'll take every precaution to get him back fully when he is able to return."

Uehara is unscored upon in his first five appearances this season, with two saves. In five innings pitched, he had struck out seven, had not walked a batter, and had allowed just three hits in 19 at-bats.

"His daily routine is to throw long toss out to 200 feet," Farrell said when asked what the plan is for Uehara on Sunday. "That's common to him. Whether or not he completes that remains to be seen. That's the initial plan."

The Red Sox are off on Monday before opening a three-game series against the White Sox on Tuesday in Chicago.

"It's another day available to us," Farrell said. "Based on the information we get tomorrow, that gives us the possibility of him returning to Boston to be checked out. That's not set in stone yet, but it's a possibility. We're still gathering information."