WASHINGTON — The Nationals announced Thursday that Stephen Strasburg has a flexor mass strain in his right arm but no tear of the ulnar collateral ligament. There is no timetable set for his return.

Strasburg exited Wednesday night’s start, his first since returning from the disabled list, in the third inning after just 42 pitches. He was seen wincing in pain on his final three pitches, making a fist and flexing his right forearm on the last two, eventually signaling to the dugout.

Strasburg tore his UCL in his rookie season in 2010, and there was fear he had done so again Wednesday night. The recovery time for Tommy John surgery is usually around one calendar year, but can range up to two years with complications. While roughly 80 percent of pitchers return after their first UCL replacement surgery, that figure drops to somewhere around 25 percent on a second procedure.

The Nationals signed the 28 year-old Strasburg to a seven-year, $175 million extension this May. He is 15-4 with a 3.60 ERA in 24 starts this season.