Gallup suffered the injury during the fourth quarter of Sunday's 31-21 victory over the Washington Redskins. Although there was optimism after the game, further testing Monday revealed a cartilage issue.
Through two games, Gallup leads the Cowboys with 13 receptions for 226 yards. He had a career-high 158 yards on seven catches in the season opener against the New York Giants. While Gallup is out, the Cowboys have Randall Cobb, Devin Smith, Tavon Austin and Cedrick Wilson to play opposite Amari Cooper.
"[We] feel good about the guys we have," Garrett said. "Devin obviously will play more. Cedrick will have an opportunity. We're still waiting on Tavon, so hopefully Tavon is back and those guys can just step into those roles."
Austin did not play against Washington because of a concussion, but Smith caught three passes for 74 yards, including a 51-yard touchdown in the second quarter. Cobb has the most experience and has nine catches for 93 yards and a touchdown so far. Wilson opened the season on the practice squad but was called up for the Washington game to replace Austin.
"I think we feel good about how those two guys performed yesterday," Garrett said. "They got a chance to go in there and play and they stepped up and you just have to keep kind of giving them shots and hopefully their confidence will build as they go."