From cubs.com...

"Chicago Cubs center fielder Corey Patterson had to leave Monday's
game when he was hit on the right knee by a pitch from Texas' Nick
Regilio.

"I think it sounded a lot worse than what it was," Patterson said.
"I'll be OK."

Patterson returned to Mesa, where he was examined by the team's
medical staff, then sent home.

The incident occurred in the second inning. Patterson, 25, fell to the
ground immediately and Cubs manager Dusty Baker rushed to his side.
The center fielder was pulled from the game but able to walk off the
field and into the clubhouse under his own power.

"The ball was running in and I tried to get out of the way from it and
there was no chance," Patterson said. "[Tuesday] might be a little bit
worse. I think overall I'll be OK. It wasn't like a couple years ago."

In July 2003, Patterson suffered a torn anterior cruciate ligament in
his left knee running to first base. He missed the rest of the season."