The 23-year-old loose-head prop hobbled off the pitch during their Dragons' narrow win over Connacht with damaged knee ligaments and faces a lengthy spell on the sidelines.
Gustafson will miss the Men of Gwent's upcoming European fixtures and faces a race against time to be fit for the games Magners League games with Edinburgh and Aironi.
He was an ever-present feature in the Dragons' side last season making 26 out of their 28 games but they have been boosted by the return of Phil Price who has made two appearances off the bench after recovering from a rib injury.
"It's a blow losing Hugh, but we are where we are without props and Phil Price is fit again and playing well," said Dragons head coach Paul Turner.
But in a boost to the Dragons and Wales Turner expects to have flanker Dan Lydiate back fit for the weekend.
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland