Witten suffered a "very serious" small laceration that caused bleeding but it is not ruptured, coach Jason Garrett said Wednesday afternoon.
Witten is not expected to undergo surgery, but the Cowboys will proceed cautiously and not allow him to participate in contact drills and want him to be "still and idle" for 8-10 days before being re-evaluated, Garrett said.
Witten will miss the remainder of the preseason, and "it will be very close" as to whether he plays in the Sept. 5 season opener against the New York Giants, according to the source.
One of the Cowboys' offensive captains, Witten was present at the team's practice Wednesday. He watched the morning walkthrough for about 25 minutes and left before the practice was completed.
Witten suffered the injury after taking a hit from Oakland Raiders linebacker Rolando McClain in the first quarter Monday, multiple sources said. Witten missed a few plays but returned and caught one more pass before the first-team offense called it a night.
Witten said he was OK after the game, but Cowboys owner and general manager Jerry Jones admitted some concern when he saw the seven-time Pro Bowler leave the contest.
Losing Witten would be a major blow to an offense that relies on him heavily in the run and passing games. He has become the go-to guy for quarterback Tony Romo, catching 409 passes for 4,824 yards and 21 touchdowns since Romo took over as the starter in 2006.
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