Sometimes it’s easy to forget the physical strains and unbearable pains that professional athletes put themselves through.

Just over a year ago Novak Djokovic was the dominant force at the head of men’s tennis. He held all four grand slam titles and was the undisputed world number one. Maybe now, we’ll appreciate his phenomenal achievements a little more.

It was a sombre sight watching the 12-time major champion yesterday, as he was forced to retire from his Wimbledon quarter-final against giant Czech Tomas Berdych.

The Serb had required treatment on an elbow injury after losing the first set tie break, before deciding that he couldn’t continue when trailing 7-6 (7-2) 2-0.

Berdych will now face Roger Federer in the semi-finals, after the Swiss defeated Milos Raonic 6-4 6-2 7-6 (4).

"It has bothered me for over a year"

Djokovic had also suffered a shoulder injury in his previous victory over Frenchman Adrian Mannarino.

In the Serb’s post-match press conference, he revealed that his elbow had troubled him for some time.

"I haven't felt this much pain since I've had this injury," said Djokovic. “It’s not the shoulder, it's the elbow that has kept bothering me for over a year and a half.

"I was able, for 30 minutes, to play with some pain that was bearable, but the serve and forehand were shots where I could feel it the most. After that, there was really no sense.”

Djokovic follows Murray out of Wimbledon

The result came just a few hours after defending champion Andy Murray crashed out of the men’s singles competition, losing in five sets to the big serving American Sam Querrey.

Murray, too, was clearly struggling physically, as he lost the fourth and fifth set in under an hour.

It had been known since the start of the tournament that Murray was carrying a hip issue, which had hampered his preparation ahead of the third major of the year.

Djokovic’s injury came as more of a surprise, especially after the 30-year-old won the title in Eastbourne the week before Wimbledon.

However, this was the Serb’s second match in the space of two days, after his match with Mannarino was delayed until Monday.

Djokovic managed to hold serve comfortably in the first set, however after losing the opener on a tie break, he began to show visible signs of pain.

His first serve speed dropped and, after falling behind at the start of the second set, the Serb decided that it wasn’t worth the risk.

Federer still yet to drop a set

Wednesday’s results mean that Federer is now the overwhelming favourite to claim the men’s title on Sunday.

The 18-time grand slam champion was in imperious form as he dismissed Raonic, the man who defeated him last year, in one hour and 58 minutes.

It means that Federer is still the only man yet to drop a set at this year’s championships.

In the other semi-final Querrey will face Marin Cilic, who defeated Rafael Nadal’s conqueror Gilles Muller in five sets.

Both will be bidding to reach their first final at the All England Club.