Boris Becker considers Roger Federer to be on a par with sporting icons Muhammad Ali, Michael Jordan and Pele for his achievements in tennis.
Federer, 35, endured an injury-plagued 2016 but returned in scintillating fashion this year, winning his 18th grand slam title at the Australian Open and following it with ATP Masters 1000 triumphs in Indian Wells and Miami.
Becker, a six-time major winner, believes Federer's resurgence reaffirms his status as the best player in history and earns him a special place in the pantheon of sporting greats.
"If you would have asked him would he be winning the Australian Open, Miami and Indian Wells Masters he probably would have laughed but Roger Federer is the all-time greatest," Becker, a Party Poker ambassador, told Omnisport.
"We shouldn't be surprised by anything Roger does. At 35 years of age he is one of the greatest sportsmen of all-time in the league of Ali, Jordan and Pele."
Federer has taken a break from the ATP circuit to avoid injury ahead of the French Open, though he has suggested he could skip Roland Garros if he does not feel "fired up" for it.
Whether he features or not, Becker does not believe 12-time grand slam winner Novak Djokovic and Rafael Nadal - defeated by Federer in the Australia and Miami finals - can be discounted.
He said: "You should not overlook Novak Djokovic, he's the defending champion and you should never overlook the defending champion.
"But Rafael Nadal has had a wonderful season. Finals in Melbourne and Miami and clay is his favourite surface and he's a nine-time French Open winner so [his chances are] pretty good."