Manager David Moyes confirmed both Rooney and strike partner Robin van Persie will miss Saturday's Premier League encounter with Swansea at Old Trafford.
Moyes said Van Persie would still be absent for "a little while" with a long-standing thigh injury, while hoping Rooney would respond to the better temperatures.
"We have sent Wayne away on a hot weather break," said Moyes.
"His groin has not quite recovered yet.
"We have sent a fitness coach with him. He's away with the family. Hopefully we will get him fit for Chelsea."
Rooney has missed United's defeats to Swansea and Sunderland in the last week, having had a scan on his groin injury last Friday.
Van Persie has not featured since the home defeat by Newcastle on December 7, his only game since the middle of November.
"Robin is not available," said Moyes.
"He is going to be a little while. We are doing everything we can to get him back as quickly as we can."
It means United will be without seven senior stars for the Swansea game, with Rio Ferdinand, Phil Jones, Marouane Fellaini, Nani and Ashley Young also sidelined.
But with Rooney at least, Moyes felt there was no option.
"It is the right time,'' he said. We have given it a chance to heal."
Looking to avoid a fourth successive defeat for the first time since 1961, it is hardly the news Moyes was hoping for.
Yet the Scot insists it is nothing new.
"If you go into football management, you are going to lose games. I don't know any football manager who hasn't,'' he said.
"You have to go through it at some time in your career.
"I have had equally challenging times at other times in my career.
"We are having a difficult time just now. There is a lot of attention but that is to be expected.''