Nationals general manager Mike Rizzo confirmed that, yes, Stephen Strasburg will be headed to the disabled list. However, he did not rule out Strasburg returning to pitch this year.
Via Mark Zuckerman:
Rizzo: #Strasburg MRI shows strained flexor tendon. He'll get enhanced MRI in next couple days. Wouldn't rule out pitching again this year.
Rizzo added that Strasburg had the same issue in college and that both MRIs will be done locally (so no Dr. James Andrews), according to Nationals News Network.