"It just felt like I cramped up a little," Paxton said. "I'm going to get an MRI tomorrow to see how serious it is. I don't think it'll be anything too serious and, obviously, I don't want to miss time right now, so hopefully it's nothing big."
Paxton was trailing 3-0 at the time. The big southpaw winced after throwing his 107th pitch of the game and Mariners athletic trainer Rick Griffin and manager Scott Servais quickly went to the mound and took him out after a brief conversation.
"Our pitch limit for him is 110 and that's probably going to be his last hitter, which hurts even worse," Servais said. "He was throwing the ball fine. The velocity was there, everything was good. There was nothing leading up to that that made me think there was any issues at all. I saw him kind of shake his arm a little bit and that's why [catcher Mike] Zunino went out there and called us out.
"I feel bad for him. Hopefully he's not out too long."
Paxton gave up two home runs to C.J. Cron and Andrelton Simmons, snapping an MLB-leading 46 1/3 innings without a homer, but didn't seem to be in any distress until his final pitches to Kole Calhoun midway through his last at-bat.
"I felt a little off, but nothing crazy," Paxton said of his overall effort. "I made some mistakes and they made me pay early with the home runs. I just threw some pitches to bad spots and they did what they're supposed to do with those mistakes. I wasn't quite as sharp.
"It just felt like I was pulling across my body a little and cutting some pitches off. I wasn't getting the fastball to the inside corner very well, I was missing over the plate. But that's normal stuff that happens here or there and I can fix that in the bullpen."
The bigger question now is whether Paxton will be able to make his next scheduled start Tuesday against the Orioles.
"I'm hoping I wake up tomorrow and it feels fine, but I just don't know," he said. "We'll have to re-evaluate tomorrow."
Paxton allowed five hits and three runs, with one walk and six strikeouts as his ERA bumped up to 2.78, which is third in the AL behind Boston's Chris Sale (2.57) and Cleveland's Corey Kluber (2.65).
Greg Johns has covered the Mariners since 1997, and for MLB.com since 2011. Follow him on Twitter @GregJohnsMLB. This story was not subject to the approval of Major League Baseball or its clubs.