Cowboys wide receiver Michael Gallup suffered a significant left knee injury on a touchdown catch against the Cardinals and his season is likely done.ProFootballDoc, Dr. David Chao, said he has significant worry for a torn left ACL for the 25-year-old.By video, Gallup jumped and twisted for the touchdown catch, then remained down on the field. As he planted his foot at the three-yard line, his left knee appeared to buckle.Medical staff performed the Lachman test on the field to check the structural integrity of his knee, a key sign indicating an ACL injury.Sometimes the Lachman test is precautionary, but usually an ACL tear is fairly obvious on the field, Chao said.If the injury is confirmed, Gallup's season is done and he would face an uphill battle to be ready for training camp, Chao said.Gallup is a free agent this offseason.He finishes the season with 35 catches for 445 yards and 2 touchdowns in eight games played. He missed seven games early in the season with a calf injury he suffered Week 1.Update:The injury has been confirmed by the media and Cowboys owner Jerry Jones. The pending free agent will miss the rest of the season as the injury requires surgery.