Tennessee's leader went to the locker room early on Saturday afternoon.
"That's why he's here," Vrabel said of Gabbert's performance. "That's his job is to be ready to go, to prepare like a starter, and then if his opportunity comes, to come in and make the most of it. Really proud of him."
Gabbert has played in place of Mariota this season -- who suffered a nerve injury in his right elbow and left Tennessee's odd Week 1 loss to Miami -- starting two games and appearing in a total of six.
Speaking of the Colts, Tennessee (9-6) finishes the season with a critical home test against Indy (8-6) next Sunday, potentially with the No. 6 seed on the line. It remains to be seen whether Mariota will be available.