WASHINGTON -- Stephen Strasburg is going back on the 15-day injured list with a stress reaction in his second and third ribs, less than one week after returning from being sidelined for a year.

¡°He was coming along, and he was doing well and he felt good,¡± manager Dave Martinez said pregame Tuesday. ¡°Now, all of a sudden, here we are again. I feel for him, I really do. But I hope that he¡¯ll be back -- hopefully sooner than later -- but regardless of time, that he¡¯s back and he¡¯s helping us win games.¡±

Strasburg, who was scheduled to start on Tuesday, had experienced discomfort after throwing his bullpen session on Saturday. He underwent an MRI on Monday, which revealed the stress reaction related to his thoracic outlet recovery. There is no timeline for his return, and he will seek a second opinion from specialist Neal ElAttrache in Los Angeles.

¡°I¡¯m going to be, as I always am, [hopeful] that he¡¯s going to pitch again,¡± manager Dave Martinez said Tuesday. ¡°I hope that that¡¯s the case.¡±

The 33-year-old right-hander had returned to the mound on Thursday, giving up seven runs on eight hits and two walks over 4 2/3 innings against the Marlins. Aside from fatigue in his legs, Strasburg told Martinez he felt good following his season debut.

But on Sunday, Strasburg alerted the team ¡°he didn¡¯t feel right.¡±

¡°I want to look at it as, he worked really hard to come back and he was able to pitch again in the big leagues, right, even though it was one start,¡± Martinez said. ¡°Let¡¯s see what happens after this little stint here and see if we can get him back. But, like I said, we all hurt for him because he worked his butt off to get back and try to help us.¡±

The past two years have been marred by injuries for Strasburg. His 2020 season was limited to five innings because of carpal tunnel surgery in his right hand, and the following season was cut short at 21 2/3 frames for thoracic outlet surgery. Strasburg rehabbed diligently this spring at the Nationals¡¯ training complex in West Palm Beach, Fla., and he tossed three Minor League rehab starts before being reinstated.

¡°Like I¡¯ve said before, there¡¯s so many unknowns about this surgery and what can happen, and this is part of it,¡± Martinez said. ¡°It is related. We¡¯re at a point now where, honestly, Stephen¡¯s put all the work in. He¡¯s done everything that he needed to do, and this surgery, you don¡¯t know where it¡¯s going to go.¡±

When healthy, Strasburg can anchor a starting rotation. After going 5-0 in the postseason and being named 2019 World Series MVP, he inked a seven-year, $245 million contract with the Nationals. Strasburg¡¯s long-term health outweighs him pitching through discomfort in the here-and-now.

¡°For me, he deserved that contract, he really did,¡± Martinez said. ¡°You look at what he did. If it wasn¡¯t for him, we don¡¯t win a world championship. Nobody could predict what was going to happen. I just hope that the results are something that¡¯s positive from the next visit to the doctors, and then we can figure out what¡¯s next for him.¡±

In the meantime, the Nationals filled Strasburg¡¯s spot in the starting rotation on Tuesday by calling up right-hander Jackson Tetreault from Triple-A Rochester to make his Major League debut. Tetreault, 26, is 5-3 with a 4.19 ERA across 12 starts (58 innings) this season with the Red Wings.

As the Nationals look for solutions to fill a short-handed pitching rotation with a schedule of seven games in the next six days, Strasburg will seek out information on his next steps.

¡°As you know, Stephen, he doesn¡¯t show a whole lot of emotion,¡± Martinez said. ¡°I talked to him briefly yesterday, but he¡¯s a bit down. He wants to figure this out. He desperately wants to figure this out and see what¡¯s going to happen.¡±