SEATTLE — San Diego ace Jake Peavy will miss his scheduled start tomorrow night against St. Louis with soreness in his pitching elbow.

Instead of preparing to face the Cardinals, the reigning Cy Young winner will visit with Padres' team physicians Monday morning, trying to determine the root of the discomfort Peavy has experienced in his elbow during his last three or four starts.

"It's not like a normal soreness. That's obviously the reason we're missing the start is because it's not normal," Peavy said before Sunday's interleague series finale in Seattle. "Your arm is sore all the time, but I do feel some of it in the elbow (and) that's always a cause for concern. We don't know how big, but it's always better to be safe than sorry."

Peavy has lost three of his last four decisions, but his noted sharpness with all his pitches has been absent. Peavy said that's in part due to his decision not to throw bullpens in between his start, hoping that throwing less would reduce the discomfort.

And it's not just one pitch. Peavy notices the issue in his elbow on every throw.

"It's to the point now where we need to take a step back," Padres' manager Bud Black said.

Peavy is 4-3 this season with a 2.91 ERA, but hasn't pitched beyond the sixth in any of his last three starts, and lasted just four innings last Wednesday against the Chicago Cubs. Last year, he became the fourth Padres' pitcher in club history to win the Cy Young, going 19-6 with a 2.54 ERA, and leading the league with 240 strikeouts.

Peavy will have an MRI Monday morning, with the team hoping to know his prognosis later Monday or Tuesday. Left-hander Wil Ledezma will move from the bullpen to start in Peavy's place against the Cardinals.

Peavy on Sunday referred to 2004, when he missed about six weeks with a strained tendon in his forearm, but returned to go 10-3 in 16 starts after the All-Star break. Peavy's hoping whatever is causing the discomfort doesn't sideline him for that long.

"Anytime you're told you're going to miss a start and you're going to have an MRI, there is always concern," Peavy said. "But like I said, I hope everything turns out all right tomorrow."