TJ McDonald was forced out of the St Louis Rams' defeat to the San Francisco 49ers last night with a broken leg.
The rookie safety was carted off the field during the third quarter of the 35-11 loss.
NFL.com reports that the 22-year-old, who was fitted with an air cast before leaving the field, has been diagnosed with a fracture.
McDonald, who has made 18 tackles this season, was a third-round Draft pick earlier this year.
