Red Sox reliever Garrett Whitlock was placed on the injured list with right pectoral tightness. Colin E. Braley/Associated Press

The Red Sox will have to chase a playoff berth without their best young reliever.

Garrett Whitlock, who left Sunday’s win over the Orioles with right pectoral tightness, is heading to the injured list. Red Sox Manager Alex Cora said the injury is not serious, but they don’t expect Whitlock to return this week.

Whitlock was put on the IL retroactive to Monday, which means he could be back before the end of the season. Cora expects the rookie to pitch again in the regular season.

“We believe so,” Cora said.

The Red Sox recalled Ryan Brasier from Triple-A Worcester to fill Whitlock’s spot.

Whitlock, who the Red Sox took in last year’s Rule 5 draft, has been the Red Sox’ best surprise this season.

The rookie’s 1.99 ERA in 721/3 is the third-best mark in baseball among pitchers who have thrown 70 innings, and he’s been a critical piece to Cora’s bullpen in multi-inning and high-leverage situations.

He’ll be a tough loss over the next week as the Sox play pivotal games with postseason implications.

“We’ve got some capable guys and somebody has to step up,” Cora said. “We’ve got Tanner (Houck) down in the bullpen. He’ll do his job back there and we have some guys that actually were able to reset over the weekend, staying away from them. They’re fresh.

“It doesn’t matter who you lose now, it’s a big hit anyway. Whoever you lose on the roster now is a big one. It can be your star player or your utility guy. You don’t want to lose guys. Somebody else has to step up. I think we’ve done a good job throughout the season and especially the last 15, 20 days to do that. The next guy has to step up and do the job.”

NICK YORKE HAS been named the Red Sox’s 2021 minor league Offensive Player of the Year as expected.

The 2020 first-round pick had a monster season in his first year of professional baseball. He batted .325 with a .412 on-base percentage, .516 slugging percentage, .928 OPS, 14 homers, 20 doubles, five triples, 76 runs, 62 RBI and 13 steals in 97 games (442 plate appearances).

He began the season at Low-A Salem. He played 76 games there, then earned a promotion to High-A Greenville where he slashed .333/.406/.571/.978 with 11 extra-base hits in 21 games.

The 19-year-old second baseman struck out just 15.6% of the time and had an 11.8% walk rate.

Yorke started slow during May, but he then went 79-for-212 (.373 batting average) with a .467 on-base percentage, .608 slugging percentage, 1.075 OPS, 10 homers, 12 doubles and four triples in his final 55 games with Salem.

Brayan Bello was named Red Sox minor league Pitcher of the Year. The righty, who turned 22 in May, went 7-3 with a 3.87 ERA and 1.28 WHIP in 21 starts combined between Greenville and Double-A Portland.

Bello throws a fastball reached triple digits this season. His plus changeup has late fade. He also throws a slider.