Vikings coach Mike Zimmer joins NFL Insiders to reflect on trading for QB Sam Bradford and discusses Teddy Bridgewater's rehab for his knee injury. (1:42)

Teddy Bridgewater's future with the Minnesota Vikings remains murky, as the quarterback recovers from a torn ACL and left knee dislocation.

Coach Mike Zimmer said Thursday there were still too many factors in Bridgewater's recovery to commit to a specific date for his return.

"He's doing well," Zimmer said, "but we don't know when he'll be back."

Teddy Bridgewater tore his ACL and dislocated his left knee in the Vikings' final preseason practice last Aug. 30. Brace Hemmelgarn/USA TODAY Sports

Bridgewater, 24, was injured during a non-contact drill at practice on Aug. 30, ending his 2016 season. He was entering his third season in the NFL, and the Vikings were counting on him to take major steps forward after a promising start to his career.

Sam Bradford joined the team in a trade Sept. 3 with the Philadelphia Eagles and threw for a career-high 3,877 yards this season, finishing with 20 touchdowns against 5 interceptions. Zimmer said at his season-ending news conference this month that Bradford "has earned the right to be the starting quarterback" after setting an NFL single-season record with a 71.6 completion percentage.

Zimmer would not say Thursday whether Bridgewater would be ready for the start of the season.

"Teddy, I would never bet against this guy," Zimmer said. "He's got a smile on his face, comes in and works hard every day."

Bradford is signed through the 2017 season, and general manager Rick Spielman said before the season that the quarterback's contract was part of the reason the Vikings were willing to trade a first-round pick and a 2018 fourth-rounder to the Eagles for him.

Bradford will have an $18 million cap hit next year, with $4 million coming in a roster bonus due in March. The Vikings will eventually have to decide whether to sign him to a long-term contract.

Bridgewater is under contract at $2.18 million for the 2017 season. The Vikings will have to make a decision on his fifth-year option in May.

Bridgewater has not talked to reporters since his injury. He declined interview requests during the Vikings' final open locker room session of the season. The Vikings said on Sept. 9 that Bridgewater had a multiligament reconstruction of his left knee, but they have not disclosed which ligaments Bridgewater needed repaired other than his ACL.