Sportal.co.nz 14.Feb.2013Getty Images
Cowan suffered knee ligament damage during Gloucester's 27-11 win over Northampton on Saturday.
Gloucester rugby boss Nigel Davies told thisisgloucestershire.co.uk Cowan would be out of action for six months.
"It's ligament damage and we're probably looking at five to six months," Davies said.
"He's very positive in fairness to him, he's a real competitor.
"He just wants to play and he's going to do everything he can to get back as quick as he can."
David said Cowan was in a good frame of mind and determined to find his fitness before the season is over. Gloucester's medics would be doing everything to assist him in that goal but Davies admitted the chances were slim.
The injury occurred when Cowan landed awkwardly when covering loose ball.
"We're planning for the worst but hoping for better than that and he'll be battling to be back before the end of the season.
"It's horrible luck for Jimmy, and we all hope he can make a swift recovery," he said.
Cowan has made 15 appearances since joining the side in January. The club is sitting in fifth place on the premiership table eight points behind leader Leicester.