The news could not have come at a worse time for the Vikings, who are gearing up to face the division-leading Green Bay Packers Sunday.
Diggs, sixth in the National Football League with 395 receiving yards, is dealing with a groin injury he said wasn't as bad as the strain that held him out of one game in 2016.
Asked if Bradford still had a chance to play, head coach Mike Zimmer said, "I don't know, we'll see".
When Bradford returned for the Vikings' Week 5 clash with the Chicago Bears, he looked less than 100 percent, and Case Keenum replaced him with 25 seconds left in the first half of what proved to be a 20-17 victory.
Bradford has only played in two games this season.
In Diggs' absence, Adam Thielen, Laquon Treadwell and Michael Floyd will have to pick up the slack.
The Vikings and Packers kickoff at noon on Sunday at U.S. Bank Stadium.
Bradford started and played very well in Week One, but he suffered a knee injury that caused him to miss the next three games.