Peel, 26, was immediately replaced at half-time and joins his Llanelli Scarlets half-back partner Stephen Jones (bruised thumb) on the sidelines. The pair will miss the Scarlets' away trip to Connacht tomorrow (Fri) although fly half Jones is expected to be fit within the next 10 days.
But Gatland will be more concerned with Peel's fitness as the Scarlets nervously wait for a medical update on their star number nine.
Scarlets Assistant Coach Paul Moriarty said: "We don't know the full extent of Dwayne's injury yet."
Kiwi Gatland takes charge of his first match when Wales open their RBS Six Nations campaign against arch rivals England at Twickenham on February 2nd.