Ritchie initially had surgery in October after being hurt in a challenge by Leicester's Hamza Choudhury. However, he's had to go under the knife for a second time after feeling discomfort on his return to training.
Speaking at his pre-match press conference on Friday ahead of Saturday's Premier League clash with Manchester City, Bruce said: "We're all disappointed.
"There's nothing worse for a player than when you've had an operation like he'd had and the surgeon decides that he needs to do a little bit more.
"Look, we're devastated and so is he. We did give him a period of rest, he went to see the specialist again and had the operation again the next morning.
"Unfortunately, that's what it is. We hope this time that he's back in training in early January - and it's nothing too horrific, so they say. Let's hope this time it's done the trick."
Asked what the problem was, Bruce added: "A tiny fragment, a piece of bone had obviously come away with the impact, and they've gone into the tendon to remove it.
"Listen technically-wise, I'm not clued-up on the technicalities of it. We thought that he'd done it the last time and obviously the surgeon has decided to do a little bit more, and we hope that does the trick."