The 23-year-old went down without contact while trying to make a tackle on Warriors centre Rocco Berry in their Auckland NRL pre-season game on Saturday.
Gilbert's knee twisted and he could be seen screaming in pain as he fell to the ground, before being helped off the field by two medical team members.
Initial tests indicated he had torn the anterior cruciate ligament, a season-ending blow the club fears.
Tom Gilbert in action for the Dolphins before his injury against the Warriors. (Darren England/AAP PHOTOS)
A lengthy spell out would be a cruel turn for the Dolphins entering their second season.
But even more so for Gilbert, who missed more than half of the 2023 campaign after a shoulder injury sustained in State of Origin required surgery.
He didn't start Saturday's contest and had made only one run before his injury, in what was his second game back from a shoulder reconstruction.
"He's in there pretty disappointed at the moment, obviously just coming back from last year's injury in the Origin," Dolphins assistant coach Nathan Fien said post-game.
"He's a big part of our team and we are just gutted for him at the moment but obviously we just have to wait and see what the scans say."
12°C