NEW YORK -- The Yankees have six regular-season games remaining, and with closer Clay Holmes expected to be unavailable until at least the American League Division Series, they must iron out an alternate road map to the ninth inning.

Holmes sustained a right shoulder strain during an appearance in the Yankees' 3-2 loss to the Blue Jays at Rogers Centre on Monday. An MRI revealed the strain and Holmes received a cortisone injection, but manager Aaron Boone said Friday that there is no guarantee Holmes will be ready for Game 1 of the ALDS, which opens on Oct. 11.

"The first game in Toronto, I just felt a little more than normal soreness," Holmes said after the Yankees' 2-1 loss to the Orioles on Friday night. "I was able to pitch with it, but it's a spot where maybe I felt like I wouldn't be quite as effective the next inning. It's nothing too worrisome, but where we are in the season and with the workload that's coming, we want to play it smart before the postseason."

Holmes said he is "very optimistic" that he can return in time for the ALDS. An American League All-Star for the first time this year, Holmes is 7-4 with a 2.54 ERA in 62 appearances, converting 20 of 25 save opportunities.

"I would say he's unlikely to get into one of the last six [regular-season] games," Boone said. "It's a concern, but I feel like we're trending in a good direction. I think the biggest thing for us is, is he going to be ready for those first two games in the Division Series? That's kind of the timeline it seems like we're on right now."

If Holmes is unavailable, the Yankees could ask for higher-leverage innings from Scott Effross, Jonathan Loáisiga, Ron Marinaccio and Lou Trivino.

"We've dealt with this all year, with the bumps in the road," Marinaccio said. "We feel like we've got the guys down there that are ready to jump into [any] spot and take over whatever we need."

Boone revealed Holmes' injury on a night when Zack Britton faced two batters and exited with what the club described as "left arm fatigue." Britton was placed on the injured list prior to Saturday's game, effectively ending his chances of contributing on a postseason roster. The Yankees purchased the contract of right-hander Jacob Barnesto take Britton's place in the bullpen.

"Basically, it's just something that he's kind of run out of time here," Boone said of Britton. "Having a little bit of fatigue last night, you don't want to power through that and reach for more and then do some damage. He's in a good spot [physically] heading into the offseason."

However, Boone said that he was pleased to see Aroldis Chapman toss a scoreless eighth inning on Friday, which included a pickoff of Rougned Odor at first base. Chapman is attempting to secure a postseason roster spot after missing time with an infection.

"He didn't have his great fastball, came in and fell behind, and was still able to navigate to get back in the count," Boone said. "He made some pitches. On a night when he didn't necessarily have his really good stuff, he was able to navigate. That's important."

The Yankees do believe that Wandy Peralta will return from the injured list when eligible on Oct. 4, expecting to place the left-hander on their ALDS roster.

"We're trying to get them all healthy and ready," Boone said. "We still feel like we have really good options down there. There's no use crying about what you do or don't have. You've got to make the most of what you do. The reality is, we still have a lot of talented guys down there."