Markstrom underwent an MRI on Monday after suffering the injury in a 9-3 win over Boston on Saturday.
Backup Thatcher Demko will receive the bulk of the workload in Markstrom's absence. He started and made 37 saves en route to the Canucks' 4-3 overtime win Tuesday in Montreal.
"I want the guys to have confidence in me," Demko said after the win over the Canadiens. "This being the first game of the stretch, it was an important game for me to come in and just kind of calm the group. If I don't play well, maybe they get a little bit nervous for the next handful of games. It was good for me to kind of get in a rhythm. Obviously, there's a lot more games that I'm going to be playing. I just want to keep getting better as we go."
With concern over Markstrom as the postseason push continues in a congested Western Conference, Benning dealt for New Jersey goaltender Louis Domingue just before the NHL trade deadline on Monday. Domingue, who has rotated between the Devils and their AHL affiliate this season, should slide in as the interim backup.
Markstrom stopped 34 of 37 shots in Saturday's victory over the Bruins, but briefly exited in the first period after taking a stick to the mask in a different injury. He missed 1:48 of the period. Markstrom improved to 23-16-4 with a 2.75 GAA and a .918 save percentage with the win. He has made 43 starts.
With 74 points, Vancouver was tied with Edmonton for second place in the Pacific Division as play began on Wednesday night.