Andre Agassi has described "timeless" Wimbledon favourite Roger Federer's exploits in the twilight of his career as "unexplainable".
Federer returned from injury following a six-month absence to win the Australian Open last year at the age of 35, ending a five-year wait for an 18th grand slam title.
The legendary Swiss followed that up by claiming Wimbledon glory for a record eighth time 12 months ago and took his tally of major triumphs to 20 in Melbourne back in January.
Federer again opted to skip the clay-court season to prepare himself for Wimbledon and will take some stopping as he goes in search of a 99th tournament triumph at the All England Club.
Agassi, a winner of eight grand slam titles in a stellar career, is at a loss to explain Federer's incredible achievements.
The American told Omnisport: "He is the favourite [to win Wimbledon] and watching him play, what is remarkable to me is how easy he makes it look after not competing for so long.
"It's almost as if he doesn't need to play tennis matches, it comes so natural for him. He makes it look easy, he has so many options, so as he gets older maybe if he loses half a step, it doesn't change how he plays.
"He gets more efficient it seems the older he gets, he seems timeless, it's remarkable, unexplainable."