Louis tore his ACL when he was attempting to tackle Vikings cornerback Antoine Winfield following a Jay Cutler interception. During the play, Louis was blindsided by Allen, who was attempting to make a block for his cornerback.
Louis was placed on injured reserve and will miss the remainder of the season. Louis started each of Chicago's first 11 games this season, but Gabe Carimi will now start in his place for the remainder of the season.
Louis is ticketed for free agency after this season.
Allen defended himself, saying that he was not trying to injure anybody -- and that he thought that the block was a legal one.
"I'm never trying to hurt anybody. I'm trying to make a block and spring our guy. It's unfortunate."
The Bears will face the Vikings again this season when they head to Minnesota to take on the Vikings in Week 14 on Sunday, Dec. 9.