Rooney has scored only two league goals all season but Pardew believes that may be down to the service he is getting.
"He is at the top of the pitch now and maybe he is not getting the service he would probably want," he told reporters.
"I can see a little bit of frustration in him but that makes him dangerous. Rooney has proved many times, particularly when he gets criticism, that he can deliver.
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"We'll be on our guard for Wayne. He's an outstanding player, he's the England captain and we'll give him the respect he deserves."
After an impressive start to the season, Palace have lost their last three games, including a 5-1 defeat by Manchester City in the Capital One (League) Cup on Wednesday.
They now face United and Liverpool on successive weekends.
"This little run is a real test," Pardew said.
"But I still think if a bit of fortune had gone our way we could have picked up points."
He said that United's visit would be "a great occasion", adding that it was "about time" Palace beat them.
United have lost only one of the last 19 meetings between the teams, a League Cup tie in 2011.
(Reporting by Steve Tongue; Editing by Rex Gowar)
