TORONTO -- Red Sox right-hander Walker Buehler returned to Boston on Thursday to have tests on his sore right shoulder and won't start against the Minnesota Twins on Friday, manager Alex Cora said.
Rookie Kristian Campbell, meanwhile, was scratched from the series finale against the Blue Jays in Toronto because of right rib discomfort, the Red Sox said. Rob Refsnyder came in to play left field and Jarren Duran moved from left to center.
Buehler is 4-1 with a 4.28 ERA in his six starts since signing a one-year, $21.05 million contract with the Red Sox last December. He allowed three runs and seven hits in six innings to beat Cleveland last Saturday, his third straight winning start.
"We're working on a few things regarding Walker. We'll see where we're at over the weekend," Red Sox manager Alex Cora said before Thursday's game. "He hasn't bounced back the way we wanted, so we have to wait."
Before joining Boston, Buehler won two World Series titles in seven seasons with the Dodgers.
Soreness in Buehler's pitching arm always leads to concern.
Buehler has undergone two Tommy John surgeries during his career, and the latter one in 2022 caused him to miss the entire 2023 season and make his 2024 debut in May.
Buehler last made it through a full season without issue in 2021 when he made a career-high 33 starts. He went 16-4 with a 2.47 ERA that season.
Cora said right-hander Brayan Bello will start in Buehler's place when the Red Sox return home Friday to begin a three-game series against Minnesota. Bello is 2-0 with a 3.27 ERA in two starts since being activated off the injured list because of a strained shoulder.
Campbell is batting .301 with four homers and 12 RBIs in 29 games. He signed a $60 million, eight-year contract with Boston on April 2, less than a week after making his big league debut.
The Associated Press and Field Level Media contributed to this report.