Leicester City, Tottenham Hotspur, Arsenal and Manchester City currently complete the top four positions and they play one another this weekend.
"It probably is a must-win game," Rooney told MUTV. "We want to get into that top four again and try and push as high up the table as possible. The only way we can do that is by winning games.
"Sunderland's ground is one that we've had a lot of good results at in the past, and we want a good performance, but I think on Saturday the most important thing is the result.
"They're fighting for survival and obviously they have a passionate crowd so we know it's going to be a difficult game for us."
United sealed a 3-0 victory over Sunderland at Old Trafford in September, with Rooney scoring one of the goals.