Hicks, a 31-year-old team captain, was transported to a hospital after Sunday's 27-19 win over the New Orleans Saints. He suffered a right shin contusion during the first quarter and did not return. Hicks watched the rest of the game from the sideline, but O'Connell said continued swelling in his leg caused the team's medical staff to seek further care after the game. He underwent a procedure to relieve pressure that could have been damaging, the coach said.
"You can classify it as kind of a compartment syndrome," O'Connell said, "where the pressure in that area and the damage it can cause if not handled with the utmost level of concern ... could've been very serious."
Hicks was doing well after surgery and remain hospitalized as of Monday afternoon. He will miss at least Sunday night's game in Denver, O'Connell said. Linebacker Ivan Pace Jr., an undrafted rookie, replaced Hicks on Sunday as the defensive signal caller wearing the in-helmet microphone that communicates with coordinator Brian Flores on the sideline.
On Monday afternoon, though, the Vikings added a familiar face who used to run their defensive huddle.
According to a source with knowledge of the situation, the Vikings signed Anthony Barr to their practice squad Monday afternoon, bringing back the four-time Pro Bowl choice who spent eight seasons with the team that drafted him ninth overall in 2014. Though Barr was an outside linebacker in a 3-4 defense at UCLA, the Vikings made him a centerpiece of Mike Zimmer's 4-3 schemes and paired him with Eric Kendricks on the double-A gap blitzes that the coach helped popularize around the NFL. Flores has used the blitz at times and sends extra defenders after the quarterback more frequently than Zimmer did.
If Barr, who hasn't played this season after appearing in 14 games with the Dallas Cowboys last year, is ready to contribute, he could assume part of his old role in the defense. He is the second of Zimmer's former linebackers to return to Minnesota this year, after the team brought Nick Vigil back to its practice squad.
"I can't even put into words how important [Hicks] has been," O'Connell said, "with what we do on defense, how he's communicated, played a ton of snaps for us and getting into calls in games and adjustments."