A University of Houston rushing attack that has shown improvement in recent weeks was dropped for a big loss Monday. Dillon Birden, who has split time as the Cougars' featured back, is out indefinitely with an elbow injury, coach Major Applewhite said at his weekly news conference. Birden, a walk-on who was voted a team captain before this season, suffered the injury late in the fourth quarter of Thursday's 42-38 loss to Memphis. A source said Birden tore ligaments in his right elbow and could miss anywhere from three to six weeks. "Dillon will be out for sometime," Applewhite said. "I don't know how long, but it won't be a week or two. So he'll be out for awhile." In six games, Birden was UH's second-leading rusher with 333 yards on 60 carries - a robust 5.6 yards per carry - and four touchdowns. He missed one game against SMU earlier this month with a stiff neck. With Birden out, Duke Catalon will get most of the work out of the backfield, beginning in Saturday's game against No. 17 South Florida at Tampa, Fla. In the last three games, Catalon has rushed for 314 yards and six touchdowns. He is averaging nearly 23 carries per game during that span. "Duke's got to carry a majority of the workload," Applewhite said. An area of concern for the Cougars the entire season has been the lack of depth behind Catalon and Birden. None of the three challengers - Mulbah Car, Patrick Carr and Davion Mitchell - separated themselves in camp, and they have been used on a limited basis.