Perez was scheduled to undergo an MRI exam in Cleveland on Monday afternoon.
While Perez is out, setup man Vinnie Pestano will assume the ninth-inning duties.
'We talked to Vinnie this morning," Indians manager Terry Francona said on Monday. "He's comfortable slotting into that inning, and part of the reason we're doing that is it makes it so much easier for us if you have an end point to get to. And we have plenty of depth. I still think having guys know [their role] really helps."
Perez felt a pinch in his shoulder on a 1-1 pitch to Jacoby Ellsbury with two outs and the bases loaded in the ninth inning of Sunday's 6-5 loss to the Red Sox. The closer was removed from the game after attempting a warm-up pitch, and Ellsbury delivered a walk-off double on the first pitch from Tribe side-armer Joe Smith.
Francona insisted that Perez had not been pitching through any discomfort prior to the ill-fated 1-1 offering.
"We'd never pitch somebody that we didn't think could pitch," Francona said. "His velocity was very good [on Sunday]. He was up to 94 mph. He felt it on that last pitch. We communicate a lot with these pitchers consistently. We would never pitch somebody that we didn't think we should -- ever."
On the season, Perez has posted a 4.32 ERA with six saves, 18 strikeouts and 10 walks in 17 appearances. The right-hander has allowed seven runs (four on Sunday) across his last three games, marking the first time in his career he has allowed that many runs in a three-game stretch. This is the first time since 2008 that he has allowed at least one earned run in three straight outings.
With Pestano temporarily moving into the closer's role, Smith (1.06 ERA) will likely be the primary eighth-inning arm. Francona also has other right-handed options such as Cody Allen (2.31 ERA), Bryan Shaw (1.85 ERA) and Matt Albers (3.52 ERA). To fill Perez's spot in the 'pen, Cleveland promoted left-hander Nick Hagadone from Triple-A Columbus, giving the Tribe three lefties (Rich Hill and Scott Barnes are the others).
Over the past nine games, dating back to May 18, Cleveland's bullpen has ranked 29th in the Majors with a 7.67 ERA (25 earned runs in 29 1/3 innings). That has not shaken Francona's confidence in the group.
"Our bullpen has been outstanding and will continue to be," Francona said. "I think we're in better shape than a lot of teams, even when we lose our closer. I've been on teams where you manipulate it to get to certain guys. There's not one guy out there we have to run away from. That's a nice feeling. We'll be all right."
Pestano has served as a reliable setup man for the past few years for the Indians, but the right-hander has recently dealt with injury concerns as well.
Earlier this month, Pestano spent time on the 15-day DL with right elbow tendinitis and he has posted an 11.25 ERA (five earned runs in four innings) in four appearances since being activated. On Saturday, Pestano yielded a career-worst four runs in the eighth inning of a 7-4 loss in Boston, hitting around 87-90 mph on his fastball throughout the outing.
Pestano, who posted a 2.57 ERA with 76 strikeouts and 36 holds in 70 games last year, normally sits around 92-93 mph with his heater.
"Vinnie's last couple outings since he's come back haven't been his best," Francona said. "But that will improve. And to be honest with you, Vinnie is going to pitch innings when the game's on the line. So if it's the seventh, eighth or ninth, we've got to get him out there.
"And there's some things mechanically that [he found]. I think in the near future he'll be fine."
Pestano was working on mechanical adjustments with pitching coach Mickey Callaway and bullpen coach Kevin Cash even before Saturday's rough showing. On Monday, the pitcher noted that -- from breaking down video -- he found that he has been more hunched over in his delivery lately, and his release point has shifted back too far.
"Now that I know what I was doing, it's about getting a feel for it again," Pestano said. "Once you get that feel back, you can start repeating it better."
Pestano reiterated that his elbow feels healthy.
The new closer also indicated that he has dealt with this elbow issue in the past.
"It's been something that's been lingering ever since the beginning of Spring Training two years ago," Pestano said. "But we've always been able to stay on top of it and, if it did flare up a little bit, we were able to get on medication and that would take care of it. Tendinitis is one of those things that, if it's not past a certain level, once you get hot, you don't feel it."