"It tightened up on me," Steele said after the 4-3 loss. "Was kind of throbbing a little bit but obviously wanted to keep competing and pitching. Just for precautionary reasons it made sense."
Steele, 27, was visited on the mound by the training staff in the top of the third but was able to complete the inning. He didn't come back out for the fourth as righty Hayden Wesneski took over for him.
"He didn't feel it throwing, just when he was cooling down," manager David Ross said. "Radar went way up, obviously ... The more I watched him throw, the more nervous I got with a guy like that, so just went ahead, for precautionary reasons, pulled him."
Steele has been one of the best pitchers in the National League this season, compiling a 2.65 ERA, including his three shutout innings on Wednesday. He had not allowed a runner to reach base before leaving. Forearm tightness can be a precursor to Tommy John surgery, an operation Steele underwent in 2017.
"I'm really not too concerned about it," he said Wednesday.
Steele will stay in Chicago for testing on Thursday as the team heads out on a 10-game road trip beginning in San Diego on Friday. He'll likely rejoin the team there -- depending on what the tests show. If he's unable to make his next start, Wesneski could be in line for it after throwing 59 pitches in relief.
"I don't think anyone is sounding any alarms at the moment," Ross said.
Steele has given up just 56 hits in 68 innings during his breakout season. He was a 2014 fifth-round draft pick by the Cubs.
"I felt really good today," Steele said. "It sucks."
The win by the Rays was their 40th of the season, matching the 2001 Seattle Mariners as the only other team in history to reach 40 wins before June 1.