"It's just a little strain," said the 25-year-old Canadian. "I'm going to go get an MRI to see what exactly is going on in there, but I just want to be careful right now. My strength is still good, they said, so I just want to get it checked out."
Mariners reliever Stephen Pryor missed almost all of 2013 after partially tearing his lat muscle and then having complications when he tried to return midseason, but Paxton's preliminary diagnosis indicated a strain and not a tear.
Paxton was taken out after throwing just 60 pitches. After giving up back-to-back home runs in the first to Albert Pujols and David Freese, Paxton had retired 14 straight before a leadoff single in the sixth by Kole Calhoun.
Manager Lloyd McClendon and trainer Rob Nodine hustled to the mound after the youngster shook his left arm following a first-pitch ball to Mike Trout following Calhoun's base hit. McClendon said they were watching carefully after Paxton had reacted to another pitch in the fifth.
"I saw him shaking his arm," McClendon said. "I went out, that kind of alarmed me a little bit. I knew something was up, then he told us. I think it happened the inning before, because he shook his arm once in kind of a weird way. I talked to him on the bench and he said, 'No, I'm OK.' He went back out and I didn't see that."
Paxton departed with a 4-3 lead, and the bullpen shut the Angels out to preserve his win. He's 2-0 with a 2.25 ERA on the season and 5-0 with a 1.75 ERA in his six-game career.
"In the fifth inning there, the last batter, I just felt a little tweak," Paxton said. "I felt fine between innings, so I didn't think it was going to be anything. I threw those cutters to the first hitter Calhoun, and that was fine. I just felt it again when I threw the fastball to Trout."
After a quick conversation, Paxton walked off the field with Nodine as reliever Yoervis Medina was called in from the bullpen. Paxton allowed four hits with no walks and four strikeouts in his five-plus innings.
Paxton came into the contest 4-0 with a 1.16 ERA in five career starts, including four last year as a September callup.
According to Elias, he was just the second pitcher in Major League history to go 4-0 or 5-0 in his first five games, all starts, with an ERA under 1.25. The other was Boo Ferriss of the Red Sox, who went 5-0 with a 0.60 ERA in 1945.