Sunderland's Campbell may need second knee op
"We do fear for him. We think the surgeon needs to go and have a look inside his knee again and if it does need repairing again, then Fraizer is going to miss the best part of next season as well," Bruce told reporters.
The 23-year-old Campbell has not featured for Sunderland's first team since injuring his cruciate ligament in August 2010.
The former Manchester United and England under-21 forward was close to a return earlier this month but twisted his knee in training ahead of their 5-0 loss to Manchester City on April 3.
Sunderland, who are without a win in eight games, visit fellow strugglers Birmingham City on Saturday.