There is a Uefa rule that says you can't play an FA Cup game on the same night as a Champions League fixture.
So Hull must face Brighton in the FA Cup 5th round replay on Monday night, just 48 hours after they face Cardiff on Saturday afternoon.
"It's not good for anyone to play two games in three days," Bruce said. "But there's not much we can do.
"The travelling will not go in our favour, it's not the best scenario for us but we just have to focus on this game and try to win."
Hull keeper Allan McGregor believes the game against Cardiff is huge and his side will need to improve on their trip to Brighton last Monday in the FA Cup.
"Cardiff is a massive game now, especially with everyone at the bottom end picking up points," he said. "We will have to play better than at Brighton."