MESA, Ariz. -- Mark Prior will be sidelined indefinitely because of inflammation in his right elbow, which the Cubs pitcher says is different from the discomfort he felt last spring.

Prior, who was to have started on Tuesday, underwent an MRI on his elbow on Sunday. He had felt some discomfort after his first Cactus League start last Thursday. He also was examined by orthopedic specialist Dr. Lewis Yocum.

Prior did not pitch until June last year because of problems with his right Achilles and elbow that popped up in Spring Training. He also had an MRI on his elbow in late March 2004 because of discomfort, and Yocum had looked at him then.

"Obviously, we're talking about an elbow and a matter of inches," Prior said. "It's a completely different area and not even the same thing (as last year). It's a different part of the body. It's not the same thing."

Cubs general manager Jim Hendry said Monday the MRI showed there is no damage to the ligament and no damage to the ulnar nerve in Prior's elbow.

Prior first felt the discomfort when he was doing some postgame exercises and told Cubs athletic trainer Mark O'Neal that he felt something "unusual."

"I know what I feel like after I pitch and I knew this was something that was a little different," Prior said.

Strength-wise, everything is fine, he said.

"It's just a nerve that got inflamed," Prior said. "As soon as we get it calmed down, I'll be fine.

"It's Spring Training," he said Monday. "Going out there tomorrow against the Royals isn't going to mean a lot the rest of the regular season. I'm not worried about it. I'm pretty upbeat about it and optimistic. It's not like I'm down in the dumps about it."

It's tough for Cubs fans to feel optimistic since Prior is the second Cubs starter to be sidelined this spring. Kerry Wood was scheduled to start on Monday but was scratched because of tightness in his right shoulder. Instead, he threw from about 90 feet in right field, then moved up to simulate his pitching motion from 60 feet and had no discomfort.

"You don't like to have any problems," Hendry said. "I'm optimistic that both of them will be fine. 'Woody' feels like he'll be throwing here in the next couple of days.

"At this point I don't consider 'Woody' not being ready for the first week of the season," Hendry said of his projected Opening Day starter.

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Ryan Dempster, Glendon Rusch or Sergio Mitre could fill in the rotation if Wood and Prior are sidelined at the start of the regular season.

O'Neal said Prior's MRI exam showed the symptoms were different than what the right-hander experienced last spring. The problem now, O'Neal said, is inflammation in the joint and some irritation to the ulnar nerve.

"We have to let those (anti-inflammatory) medications take effect and basically the nerve and the inflammation will dictate when we can proceed," O'Neal said. "We're going to let this thing quiet down. We don't feel it's appropriate to try to push through this now considering the history he had last year."

"It could very well be a situation that Mark may go through every spring," Cubs pitching coach Larry Rothschild said. "At least we know what the situation is. It's different from last year. At least we were able to diagnose this and treat it."

Prior had prepped for his first spring start by doing more simulated games, and Rothschild said the problem could be related to the right-hander possibly over-extending when he faced hitters in his first game.

"There are guys shut down all over the league who get shut down with stiffness and inflammation," Prior said. "I'm not alarmed or panicked. Last year I was a little nervous about it because we didn't have a clear idea of what it was.

"We have a pretty definitive answer of what it is," he said. "It's something I have to get through. I'm not really worried."

Prior, who was 6-4 in 21 starts last year, will not throw at least until Wednesday, and that would be on the side.

"I don't have a crystal ball. It's hard to speculate," O'Neal said of the perfect situation. "The best case scenario is that in two or three days, he starts playing catch and it's completely relieved and we move forward. That's just purely speculation."

Does it hurt?

"The only way I can describe it is that it feels like your funny bone," Prior said. "You know when you hit your funny bone and the next day you have that weird feeling. I don't feel it all the time. The good thing is that I don't think about it. It's not like I'm walking around and I'm being very gingerly and watching what I'm doing. We'll just shut it down until it's better."

It is a little frustrating, especially after missing all last spring because of injuries.

"It's disheartening because I felt I was having a good spring," Prior said. "I don't want to sit out. I like being out on the field. That's why we play. It's frustrating. I was little ticked off when it first happened. I think if there's anything I've learned from last year it's that I have to be patient and I have to deal with it.

"I worked out all offseason and you can't prevent things," Prior said. "I'm in the best shape I could be in and sometimes you can't prevent things."