Joeckel was injured in the first quarter of a 34-20 loss to the Rams on Sunday. He was taken off the field on a cart.
Joeckel got his leg rolled up by Rams defensive tackle Kendall Langford at the end of a 1-yard carry by Maurice Jones-Drew. He was selected by the Jaguars with the second pick in this year's draft.
"I saw it happen and it's unfortunate," said quarterback Blaine Gabbert, who also left the game with an injury. "It wasn't pretty."
Jones-Drew said he was to blame.
"It's tough when you were the guy that probably hurt him, too, which was me," Jones-Drew said. "You never want to run up anyone's back like that. He was doing so well. He was coming along."
Earlier this week, Jacksonville traded veteran left tackle Eugene Monroe to the Baltimore Ravens in exchange for multiple draft picks.
"You know what? Luke's a good player, but guys will step up," coach Gus Bradley said.
Gabbert strained his left hamstring in the third quarter. Playing in his hometown, he was 9 of 19 for 181 yards with one touchdown and two interceptions before leaving.
Jaguars tight end Allen Reisner left the game in the third quarter with a knee sprain.
Cameron Bradfield, who replaced Joeckel, has 14 career starts in three seasons since making the team as an undrafted rookie. He started 12 games last year.
"It's very devastating for him and for us as a team," receiver Justin Blackmon said. "That just gives somebody else the opportunity to come in, make plays and give them a chance to put something on film."
Austin Pasztor started at right tackle Sunday after starting the last three games at left guard in 2012.