Rooney left Bangkok last week as Chelsea arrived with a hamstring injury which has ruled him out for just under a month.
United manager David Moyes has repeatedly insisted Rooney is not for sale.
And after Chelsea boss Jose Mourinho aired his admiration for the striker last week, Hazard echoed his coach's sentiments.
"Rooney would be a brilliant signing," Hazard said. "He's a great player who has the experience and he's still only young, at 27.
"He's got a few years left to play. But it's not up to me. It's not my decision."
Hazard, who is playing under his third coach at Chelsea in a year, revealed Mourinho once tried to sign him when he was a teenager at Lille.
"He told me he'd asked Lille, but I wanted to stay there until I was 21 and develop my game," added Hazard, who moved to west London for £32 million last summer.
"I must have been 19 or 20 at the time. Real Madrid is a wonderful team, but I had so much still to prove in the French league. I stayed because I didn't want to leave too early."
Further signings are expected at Chelsea this summer after the arrivals of André Schürrle, Marco van Ginkel and Mark Schwarzer.