WASHINGTON (AP)Washington Nationals right-hander Stephen Strasburg was placed on the 15-day injured list with a stress reaction of the ribs, the team announced Tuesday.

Strasburg has made one start this season, his first since he had surgery for thoracic outlet syndrome last summer. He felt discomfort following a bullpen session and had an MRI on Monday.

”Stephen has a stress reaction in his second and third rib,” manager Dave Martinez said. ”There’s so many unknowns about the surgery and what could happen and this is part of it. It is related.”

The 33-year-old will see a specialist and there is no timeline for the pitcher’s return. Martinez said the immediate plan for Strasburg is rest.

The Nationals made a flurry of additional moves, including calling up right-hander Jackson Tetreault from Triple-A Rochester to start Tuesday against Atlanta in place of Strasburg, and designating infielder/outfielder Dee Strange-Gordon for assignment.

Strasburg, the 2019 World Series MVP, signed a seven-year, $245 million contract to remain with the Nationals after their championship season. He has made eight starts since, going 1-4 with a 6.89 ERA in those games.

”He was coming along. He was doing well. He felt good and now all of a sudden here we are again,” Martinez said. ”I feel for him. I really do and I hope that he’ll be back sooner (rather) than later regardless of time and he’s back and helping us win games.”

The three-time All-Star is 113-62 with a 3.24 ERA in his career.

In addition to Tetreault, who makes his major league debut after going 5-3 with a 4.19 ERA in 12 starts at Rochester, the Nationals called up right-hander Reed Garrett and left-hander Francisco Perez from the Red Wings.

Garrett was 4-3 with one save and a 4.00 ERA in 22 games for Rochester. Perez returns for his fourth stint with the Nationals this season and is 0-0 with a 5.06 ERA for Washington and 0-2 with a 3.12 ERA for the Red Wings.

Strange-Gordon, 34, hit .305 with two RBIs, three stolen bases and six runs scored in 23 games for Washington.

The Nationals optioned right-handed reliever Jordan Weems to Rochester and transferred left-hander Hunter Harvey (right pronator strain) to the 60-day injured list.

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