Murray faces a race against time to find both fitness and form before the Australian Open in January, having not managed a competitive outing since Wimbledon in July.
Federer, however, reported positively from his exhibition match with Murray in Glasgow when the pair played out three light-hearted sets.
“I was actually happy how he was playing,” Federer said. “Definitely he can move better, he can serve better. We know all these things. But for a start, I think it was actually quite encouraging.
“He still has a lot of time before Australia comes around but only he knows at what level he wants to return to competition.
“But I thought he was actually pretty good. I didn’t expect him to be this good yet.”
Federer was speaking at the ATP Finals in London on Sunday after he beat American Jack Sock 6-4, 7-6 (7/4).
The absence of Murray and Novak Djokovic makes Rafael Nadal his stand-out rival at the O2 Arena, although this tournament remains one of the few titles Nadal has yet to win.
The Spaniard has defended his drought by suggesting the surface be switched from hard to his favoured clay, but Federer is not convinced.
“I think it’s not the time of the year for clay,” Federer said, “so there you have it. You can do indoor clay, I guess, but that’s a bit silly. But I get his point, it’s a fair point.”
Federer is gunning for a record-stretching seventh ATP Finals title this week and while he was not at his blistering best against Sock, victory was never really in doubt.
The match was not without embarrassment, however, for the Swiss who made what was surely one of his worst ever misses when he slapped a short forehand in the net.
The error was more surprising given Sock seemed to have given up the point, turning his back to leave Federer facing his backside and with the whole court at his mercy.