Defensive end Ray McDonald's third-quarter sack could have been costly for the 49ers.

McDonald sustained a right biceps injury in the process of recording a sack of Matt Schaub in the third quarter against the Houston Texans in the 49ers' 34-3 victory on Sunday night at Candlestick Park.

The 49ers' medical staff examined McDonald on the sideline for several minutes before he left the playing field and returned to the 49ers locker room for further observation. The 49ers immediately announced that McDonald would be out for the remainder of the game.

"It just felt weird" McDonald said. "I didn't want to take any chances of going back out there and messing it up any more."

McDonald is scheduled to undergo an MRI examination on Monday.

"When I go in to get an MRI I'll have a better feel for what's wrong with me" said McDonald adding that he believes he will be fine.