Tim Henman feels Andy Murray will need to step up his form if he is to challenge again for the Wimbledon title.
All the big guns have had a chance to impress, with defending champion Murray the only one to be seriously tested heading into the weekend.
That came on Friday evening when the world No.1 narrowly avoided being taken to a fifth set by volatile Italian Fabio Fognini.
Roger Federer, Rafael Nadal and Novak Djokovic have looked strong through the opening rounds, with Nadal in particular impressing Henman.
Many within tennis felt the Spaniard’s career may have been over by the time he turned 30 because of the physical nature of his game.
But at 31 he looks better than ever and, after romping to a 10th French Open title, has now won 28 consecutive sets.
Henman – ranked British No.1 in 1996 and again from 1999 to 2005 – said: “Nadal for me has been probably the stand-out on the men’s side, he’s played fantastically well.
“I’d be very surprised if the winner came outside of the top four. They’re playing well, they’ve got the history and the experience of having won here before so it’s going to be interesting to watch.
“I think Federer and Nadal are the favourites. Andy’s just got to keep upping his game.”
Murray and Nadal are seeded to meet in the semi-finals, with Federer and Djokovic in the other half of the draw.
Those four players have shared the Wimbledon title between them for the last 14 years but have never all been in the semi-finals in the same year.
Murray’s path to the last four opened up with the elimination of Stan Wawrinka, Nick Kyrgios and Lucas Pouille.
But, after cruising through his first two rounds, he nearly came unstuck against Fognini, fighting back from 5-2 down in the fourth set and saving five set points.
Next up for Murray is another unorthodox player in Frenchman Benoit Paire, who has never been beyond the fourth round at any grand slam.