Rooney has been sent to the United States for warm-weather training and could return against Chelsea next week.
But David Moyes gave no timescale when asked about van Persie, who has played just twice in two months because of a thigh injury.
“Robin’s going to be a little while,” he said. “We’ll do everything we can to get him back.”
A groin problem has kept Rooney out of United’s last two games – an FA Cup exit against Saturday’s opponents and defeat at Sunderland in the first leg of the Capital One Cup semi-final.
“His groin hasn’t quite recovered,” Moyes said. “He’s away with his family and the fitness coach. Hopefully we can get him fit to face Chelsea.”
Another defeat this weekend would make it four in a row – an unprecedented run for the club in the Premier League era.
Moyes remains in the market for new signings, and he said: “The plan and decisions won’t change.
“It is difficult to get targets at this time. I have said that from day one. I have not said we wouldn’t be doing, it but it is difficult.”