The ball came off the bat toward Mark Prior at 117 m.p.h.

It caromed so hard off his pitching elbow that Cubs third baseman Aramis Ramirez caught the ball in the air while diving behind third base.

As Prior lie writhing in pain Friday in front of the Wrigley Field mound, the Cubs were left holding their breath.

They still are holding it. Though immediate X-rays showed no broken bones, the Tribune has learned that a subsequent MRI revealed a hairline fracture that leaves his availability for the rest of the season in question.

Prior will go on the disabled list. One source said the preliminary diagnosis is the injury should heal in three to four weeks. After that there would be a rehab period that could keep him out for up to another month.

For a pitching staff already in a shambles, that is the worst of news.

Earlier Friday, trainer Mark O'Neal said it would be tough to make a decision on what's next for Prior--who was hit on the outside portion of the elbow where two bones meet--even if the MRI were negative.

"That's a tough question, [one] everybody's going to be asking," he said. "It's really going to be determined by how sore he is, how much inflammation. If you've ever been hit by anything, you swell within the first 24 hours. We're going to have to wait and see how he is [Saturday].

"There's no way we can tell right now how long this is going to be."

Prior was injured when Brad Hawpe, leading off the fourth inning for Colorado, smashed a liner that hit his elbow. The sharp crack of ball on bone was clearly audible.

"I was scared," catcher Henry Blanco said. "It's hard to see one of your teammates out there. I didn't know what to expect going to the mound."

Ramirez said he wasn't sure what happened as the ball came toward him.

"I went after the ball, and then I saw Prior on the ground," he said. "I knew something [was wrong] because the ball was hit very hard. I've never seen anything like that."

Reliever Joe Borowski, whose right wrist was broken by a one-hopper back to the mound during spring training, said he had been hit "more times than I can count."

"Your first reaction is to throw something at it, and not necessarily your glove," he said.

The ball came straight at Prior, who stuck out his elbow in an apparent effort to deflect it.

This is another incident in what is becoming an unfortunate aspect of Prior's promising career. A trip to the disabled list would be his fifth in the last four years and his second this season.

In 2002 he missed time with a strained left hamstring. In 2003 he was sidelined with a bruised right shoulder. Last season he missed the first two months with tendinitis in his right Achilles' tendon.

It has not been a good season to be a Cubs pitcher.

For instance: - Prior was making just his ninth start because he opened the season on the disabled list with an inflamed elbow.

- Kerry Wood is currently on the disabled list with a strained shoulder and could miss another month.

- Borowski's right wrist was broken, and he has just returned to active duty.

- Another closer candidate, Chad Fox, had his season ended almost a month ago with serious elbow problems.

- Reliever Mike Remlinger was just placed on the DL with a fractured little finger on his pitching hand.http://chicagosports.chicagotribune....s-sports-print

- Starter Carlos Zambrano has avoided the DL but has been bothered much of the season by what is described as "tennis elbow."

"We've had lots of [injuries], that's for sure," first baseman Derrek Lee said. "But you can't feel sorry for yourself, because no one else will."