The St. Louis Rams have signed undrafted rookie wide receiver Danario Alexander off the practice squad, reports Brian Stull of 101 ESPN in St. Louis.

Alexander replaces Mark Clayton, who is headed to the injured reserve list with a torn patellar tendon in his right knee.

Alexander (6-5, 221) caught 191 passes for 2,778 yards and 22 touchdowns during his four-year career at the University of Missouri. Knee injuries limited his playing time until his senior season, when the first-time starter caught 113 passes for NCAA-best 1,781 yards with 13 touchdowns.

A left knee injury at the Senior Bowl required surgery that kept NFL teams from taking a flier on him in April's draft. Alexander wasn't cleared medically to return to the field until early August, and he signed with the Rams after working out for several teams at a pro day in his native Houston.

Alexander did not appear in a pre-season game, but was signed to the practice squad at the beginning of the season.