“I just felt it on that last pitch. It tightened up,” Woo told reporters Tuesday. “… Didn’t feel like I could push off the way I wanted to. … I kind of didn’t really know what was going on. I just knew it felt different than anything I felt before, so I wanted to be extra cautious about it.”

Mariners manager Scott Servais told reporters that there was “no definite timeline” for Woo’s return, but he added that the team trainers were optimistic that “he can be back pretty quickly.”

In a related roster move, the Mariners recalled right-hander Collin Snider from Triple-A Tacoma. Snider has a 3.60 ERA in five games.

Woo is 3-1 with a 1.77 ERA through eight starts this season.

It’s the latest injury setback for Woo, who was scratched ahead of his scheduled start June 11 with discomfort in his right forearm. He spent the first month of the season on the injured list with elbow inflammation, returning May 10.

“Frustrated. Disappointed,” Woo said. “Obviously been a tough season so far, just dealing with injuries. Finally feeling good, ball’s coming out well, stuff is getting back to where I feel like it could be, and then… It sucks.”

The Associated Press contributed to this report.