EDEN PRAIRIE, Minn. -- The Minnesota Vikings were without their top four safeties during their walk-through on Monday, and they definitely won't have one of them on Thursday night against the Arizona Cardinals.

Antone Exum, who has started the past two games for the Vikings, fractured a rib and injured the AC joint in his shoulder in the first quarter on Sunday, according to a league source. Exum only missed one play in the game, but wasn't able to run at full speed with the injuries he sustained. He got beat on Russell Wilson's touchdown to Doug Baldwin in the second quarter, and was trailing Baldwin in coverage on Wilson's 53-yard scoring pass to the receiver in the third quarter. Exum is expected to miss 2-3 weeks, according to the source.

Coach Mike Zimmer would not comment on Exum's injury or whether he would be available for the Cardinals game.

The Vikings were without all four safeties on their active roster during Monday's practice, but Zimmer said cornerback Terence Newman -- who stepped in at safety briefly when Robert Blanton was injured on Exum's hit on Tyler Lockett -- won't have to play the position on Thursday. That would mean either the Vikings will have two active safeties from the group of Blanton, Harrison Smith and Andrew Sendejo, or they'll make some changes to their roster. They have two safeties on their practice squad: Anthony Harris, who has been with the team since signing as an undrafted free agent, and John Lowdermilk, whom the Vikings signed to their practice squad last week.