The team placed him on the 15-day IL on Tuesday with a stress reaction of the ribs, making the move retroactive to Saturday. Manager Dave Martinez said the injury is related to the thoracic outlet syndrome that ended his 2021 season and there is no timetable for his return.
"Stephen has a stress reaction in his second and third rib,'' Martinez said. "There's so many unknowns about the surgery and what could happen and this is part of it. It is related.''
Strasburg will see Dr. Neal ElAttrache in Los Angeles to determine his next steps. Martinez said the immediate plan for Strasburg is rest.
"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.''
Martinez said Monday that Strasburg experienced discomfort Sunday after he threw a bullpen session on Saturday and was set to have an MRI. He had been scheduled to start Tuesday night against the Atlanta Braves after making his season debut last week.
The 33-year-old right-hander allowed seven runs, eight hits and two walks in 4⅔ innings against the Miami Marlins in that start, taking the loss. He also struck out five and hit a batter while averaging just 91.9 mph with his fastball.
Before that, the three-time All-Star and 2019 World Series MVP had not pitched in a major league game since June 1 last year, spending much of the time recovering from surgery on July 28 to correct thoracic outlet syndrome, a compression of nerves, arteries or veins near the neck or armpit. He had made three minor league rehabilitation starts.
The Nationals signed him to a seven-year, $245 million extension in December 2019, but because of injuries, he has made just eight major league starts since signing that contract, going 1-4 with a 6.89 ERA in those games.
The former No. 1 overall pick is 113-62 with a 3.24 ERA in his major league career.
Strasburg's move to the IL was one of several made by the Nationals on Tuesday. The team also designated infielder/outfielder Dee Strange-Gordon for assignment, optioned right-hander Jordan Weems from Triple-A Rochester and recalled three pitchers from Rochester: Right-handers Jackson Tetreault and Reed Garrett and left-hander Francisco Perez. In addition, right-hander Hunter Harvey was transferred to the 60-day IL.
The Associated Press contributed to this report.