Hernandez sprained his ankle covering home plate on a wild pitch in the fifth inning of the Mariners' 5-2 win over the New York Mets on Monday night. Hernandez, who was one out short of being eligible for a win, tried to stay in but left after a painful warmup pitch.

"Felix is OK," Riggleman said. "He thinks he'll pitch Sunday and that's his scheduled day, but I don't know that he will. Certainly I'm going to be a little more conservative than that. If we get him back a couple days after Sunday, I'd be really happy."

The Mariners said Hernandez has a mild sprain and the boot is to help prevent swelling. Hernandez did not speak with reporters before Seattle's game against the Mets on Tuesday.

"He's pretty confident he's going to be able to pitch pretty quickly," Riggleman said.

The injury was a difficult end to a terrific night for Hernandez, who hit the first grand slam by an American League pitcher in 37 years in the second inning.

Riggleman said Hernandez won't start Sunday at San Diego if he can't play catch Friday, and there are no plans to put him on the disabled list. One possible replacement for Sunday is Erik Bedard, who was scratched from his scheduled start Wednesday against the Mets after leaving Friday's outing with back spasms.

The injuries to Hernandez and Bedard strained Seattle's bullpen, and Riggleman said starter Jarrod Washburn volunteered to pitch in relief of knuckleballer R.A. Dickey on Tuesday if needed. Washburn threw 118 pitches in a no-decision at Atlanta on Saturday.