Jason Witten suffered a slightly lacerated spleen in Monday's preseason game, and the star tight end's availability for the Dallas Cowboys' regular-season opener is uncertain.

Witten suffered a "very serious" small laceration that caused bleeding but it is not ruptured, Cowboys coach Jason Garrett said Wednesday afternoon.

Garrett said it is premature to discuss Witten's availability for the Sept. 5 season opener against the New York Giants but confirmed the seven-time Pro Bowler will miss the remainder of the preseason.

Witten will be re-evaluated in a week to 10 days, and surgery remains a possibility if there is no improvement.

"It's a very serious injury and we're really taking this thing day by day," Garrett said. "He has to be very still and idle for the next week to 10 days. You won't see him out there on the practice field. He won't play in the game this week or next week.

"We've just got to make sure he heals as well as possible as quickly as possible. You can imagine spleens are internal organs, and they're serious injuries involved with those things. Asking Jason Witten to be still and idle is a hard thing. That's the biggest challenge right now, but he has to do that. He has to let time heal it."

Witten briefly was on the practice field during Wednesday's walk-through but returned to the locker room before it ended. He is expected to stay with the team in California.

The Cowboys will travel by train Friday to San Diego for Saturday's preseason game and will practice against the Chargers for two days before returning home on Aug. 22.

"He's looked as good as I've seen him look since I've been around him," Garrett said. "I don't think at the end of the day him being away from our football team and off the practice field is going to be that detrimental to him. In fact, I think it's going to allow him to get his legs back and be fresh and ready to go."