Rusedski pointed to Federer's win against Novak Djokovic at the ATP Finals, his first against the Serb since 2015.
“They don't get on great, so Federer would have loved to stop his run at the year-end No 1. We can never discount these great champions and what they can produce,” Rusedski said while commentating the ATP Finals.
“Everyone was saying it was going to be one-sided and Djokovic was going to win. But Federer showed us why he is such a great champion and you don't normally see that celebration from Federer. On top of that, Rafa was delighted because he had clinched the year-end world No. 1 title.”
Federer finished the season at No. 3 in the rankings, with his biggest title win at the Miami Masters.
Rusedski also hailed Murray's comeback from hip resurfacing surgery and said he could potentially compete for Grand Slams again.
"He's an incredible competitor. Most people would not do what he's done. It is up there, from an emotional point of view and from a satisfaction point of view, with his biggest trophies," said Rusedski. "I think he'll be competitive, but to win a major—that's hard enough if you're healthy."
Henman agreed that winning a Slam would be difficult, but noted Murray's desire and motivation during his career, which has won him three Grand Slams. The 32-year-old won Antwerp this season, just a few singles events into his comeback.
"The challenge, with the best-of-five matches, is huge, but we all know that with Andy if you say he can't do something he likes to prove people wrong," said Henman. "I think it is very unlikely but I would never with all these top people... write them off."
Rusedski agreed, saying "If you say he can't do that, it motivates him more."
The Australian Open is scheduled to be Murray's first Grand Slam on the singles front since he came back on tour.