Djokovic wasn't the only top player to succumb to injury on Wednesday.
"Sam likes the conditions here".
When he responded with two majestic forehands, one apparently defying physics as it curled around the net post, they were in raptures in the stands. Goes for his shots. "I tried what I could do from yesterday to get it in the condition where I'm able to play".
"When he's standing up on the baseline, hitting forehands, dictating, he's a very risky player".
Federer first reached the Wimbledon quarterfinals in 2001 and then won the first of five straight titles in 2003.
However, when Querrey fought back in the second, you felt this wasn't going to be quite as straightforward, even after Murray restored his one-set lead by taking the third in a tie-break.
After the Djokovic-Berdych match, Gilles Muller of Germany will see action on Court 1 against Marin Cilic of Croatia in what many believe to be the most competitive of the four Quarterfinal matches.
The world number 28 will also attempt to become the first American in the semi-finals since Andy Roddick finished runner-up in 2009.
Federer will now face Tomas Berdych in the last four after his match with Djokovic came to a premature end when the Serb retired due to an elbow injury.
The 18-time Grand Slam winner's quarter-final triumph was his 100th match at Wimbledon.
"He obviously looks after his body so well, because you get to that age at 35 and almost 36 and the way he can bounce back from tough matches".
Cilic has looked the more impressive and I feel he can gain some serious ground in the rallies if he attacks Querrey's backhand. "I'm very touched, actually, to have so much support", Federer said.
The Swiss maestro, who will be 36 next month, played his best tennis of the tournament to dismantle the big-serving Canadian - avenging last year's semi-final defeat in stunning fashion.
Djokovic was today forced to retire during the second set of his quarter-final against Tomas Berdych with what he later revealed was an elbow injury.
Djokovic said he has been suffering with an elbow injury for around 18 months and admitted his and Murray's ailments could be linked to their heavy workloads past year.
He also claimed a hole had opened up on the service line on the Centre Court.
Federer is the oldest but apparently the healthiest of the other top players in the world, contrasting past year when he tried to defend his 2015 Wimbledon title with a bad knee and bad back. "As long as it kind of comes and goes, it's fine", Sport24 quoted the 30-year-old, as saying. At stake now - a chance to reach the final where he could win his eighth Wimbledon title.