Former World No 1 Mats Wilander says he doubts either Roger Federer or Rafael Nadal can return to their previous world-beating form.
Federer and Nadal enjoyed a long reign at the top of the tennis world, racking up numerous titles and Grand Slams between them over the course of the last decade and more.
But each has struggled for both form and fitness in recent times, and they were notably absent from the season-ending ATP World Tour Finals this year.
Currently Rafa is ninth in the ATP Rankings and Roger 16th following a difficult 2016 season for both of them.
As far as Wilander is concerned, he doesn't see an easy way back for these former giants of the game.
"If we're honest, at 35 is Roger Federer going to win another Slam and threaten the top three? At times, yes, but I'm not really sure," Wilander told the BBC.
"Rafa Nadal might win a French Open or two but is he going to be threat again on hard courts? He doesn't really have the game to stay up there, so he's not going to take away the number one. Neither is Roger.
"Djokovic has been there for so long but at some point his intensity and motivation has got to slip. So who's left? Andy Murray. He has learned how you have to keep on practising harder and harder and harder, just to stay where you are."