De Kock Steenkamp has picked up a groin injury and is likely to be sidelined for a while.
He is the sixth Stormers lock out of action at present. Already on the crocked list are Eben Etzebeth, Rynardt Elstadt, Manuel Carizza, Michael Rhodes and Jean Kleyn.
The Stormers are hoping Rhodes recovers from the shoulder injury he picked up against the Crusaders a few weeks ago.
If not, coach Allister Coetzee could be forced to pick Vermeulen at lock, which would see Nizaam Carr come in as the starting No 8.
Carr made a big impact when he came on in Friday’s 36-20 loss to the Chiefs in Hamilton, scoring a try late in the second half.
Meanwhile, the Stormers are also sweating over the availability of captain Jean de Villiers and fullback Jaco Taute. Both have sore shoulders.
Juan de Jongh has recovered from his knee and is believed to be on his way to Australia.
If De Jongh is not fit enough to feature, Peter Grant could also be utilised at centre.