Mujati picked up the problem during the first half of Saints’ 17-16 defeat to Saracens at stadium:mk on Sunday.
The Bulawayo-born tighthead, who is set to join French side Racing Metro this summer, limped off to be replaced by Paul Doran-Jones.
And Doran-Jones could now get a start at Sandy Park this weekend, with Mujati out.
“Brian’s got a calf injury, he’s pulled his calf so he’ll be unavailable this weekend,” said Mallinder.
But there is some good news for Saints as forwards Christian Day and James Craig and utility back James Wilson are on the recovery trail.
Day has been suffering with a ankle injury, while Wilson has not played since the end of September due to a calf injury and Craig has yet to play this season.
“They are (close to comebacks),” said Mallinder. “It’s looking very encouraging on that side of things.
“They (Day and Wilson) are both out running and Craig is as well.”