Jacksonville rookie left tackle Luke Joeckel has hurt his right ankle late in the first quarter at St. Louis and been taken off the field on a cart.
Joeckel got his leg rolled up as he was blocking on a running play Sunday. His return is doubtful.
Joeckel was selected by the Jaguars with the second pick in this year's draft.
Earlier this week, Jacksonville traded veteran left tackle Eugene Monroe to the Baltimore Ravens in exchange for multiple draft picks.