Bryant, a first-round draft pick out of Oklahoma State, suffered a high right ankle atthe end of practice Friday.
Cowboys officials said afterwards he will likely be out four to six weeks.
Bryant suffered the injury when he and cornerback Orlando Scandrick got tangled up while trying to catch a pass that was thrown behind him.
When he didn't immediately get up, it was clear something was terribly wrong.
''(Scandrick) made a play on the ball. That's what we expect,'' Dallas head coach Wade Phillips said. ''The ball was thrown behind the guy.''
Byrant had gotten off to a strong start and was in contention for a starting position should things continue to go in the right direction, but what happens now remains unclear.
The injury could keep Bryant from playing until the regular season Sept. 12 at Washington.
''We do have an extra week (of camp), which he has taken advantage of, being here and learning all those things,'' Phillips said. ''He's actually done real well as far as assignments are concerned.''
Bryant arrived before the start of training camp after becoming the first of the NFL's first-round picks to sign his contract. He received a five-year deal that guarantees him at least $8.3 million.