"It was pretty clear just in talking to the doctors ... it wasn't a hard decision," Frazier said, adding: "It's a little more extensive, but turf toe was a part of it. ... He just couldn't put any pressure on the foot and do the things he needed to do."
Jackson was 34-of-58 passing for 341 yards and three touchdowns with four interceptions in three games this season. He was playing because Brett Favre's NFL-record streak of 297 consecutive games started ended, due to a sprained throwing shoulder and numbness in his hand.
The Vikings, unsettled at quarterback, signed quarterback Patrick Ramsey on Wednesday as insurance. Ramsey is a nine-year veteran, once a part-time starter for the Washington Redskins. He was let go by the Miami Dolphins last month and hasn't started in an NFL game since 2005.
The Associated Press contributed to this report.