Bristol captain Iain Grieve could be sidelined for up to five weeks after fracturing his eye socket.
The incident occurred in their 27-7 win over Esher on Sunday - Grieve's first game back since suffering a thigh injury in December.
"At first, I thought I had a bit of dirt in my eye but it swelled up to the point where I couldn't see at all," the 24-year-old told the club website.
"I went straight to hospital and it turns out it was more serious."
The flanker added: "It's frustrating to be out again because I had been desperate to get back to playing and helping the team."
Grieve was forced to sit out several games earlier in the Championship season because of an ear infection.
Bristol's win over bottom-club Esher extended their lead at the top of the table to 11 points with five games of the regular season left to play.