London (AFP) - Defending champion Andy Murray will retain his world No. 1 ranking if he makes the Wimbledon semi-finals Wednesday, while Roger Federer defies age and Novak Djokovic fights a shoulder injury.

Adding extra spice to Wednesday's drama is a growing concern over the state of the All England Club's famed Centre Court where, according to Djokovic, a hole has developed.

Murray, one of five men over 30 in the last-eight, faces big-serving Sam Querrey bidding to make his eighth Wimbledon semi-final in the last nine years.

The Scot is also in his 10th straight quarter-final at the tournament and has reached the last-eight at 24 of the last 26 Slams. He leads Querrey 7-1 with the 29-year-old American's only win coming in Los Angeles seven years ago.

Murray also won their previous clash at Wimbledon in the fourth round in straight sets in 2010. But the two-time champion will not underestimate the player who knocked out Djokovic in the third round 12 months ago.

"Sam likes the conditions here. Obviously a big serve. Goes for his shots. Very aggressive player," said Murray.

Querrey, the world No. 28, will attempt to become the first American in the semi-finals since Andy Roddick finished runner-up in 2009.

Federer, playing his 100th match at the All England Club, attempts to reach his 12th Wimbledon semi-final and stay on course for a record eighth title when he faces Raonic.

However, the 35-year-old Swiss star is wary of the sixth-seeded Canadian who knocked him out in the semi-finals in 2016.

Federer leads Raonic 9-3 in head-to-head meetings and has reached his 50th Grand Slam quarter-final without dropping a set.

"I can look at this quarter-final in a totally relaxed fashion. Physically I'm not fighting anything like last year with my knee," added Federer, bidding to become the tournament's oldest champion in the Open era.

Djokovic takes a staggering 25-2 career record over Czech 11th seed Tomas Berdych into his quarter-final as he eyes a potential semi-final duel with Federer.

The second seed needed a medical timeout to treat a long-standing right shoulder injury in his last-16 clash with Adrian Mannarino.

Berdych has not defeated Djokovic since 2013 but he did triumph over the Serb at Wimbledon in the semi-finals seven years ago when the Czech finished runner-up to Nadal.

In the day's other tie, 34-year-old Gilles Muller makes his maiden appearance in the last-eight after knocking out Nadal, his first win over a top five player in 23 attempts.

The Luxembourg player's only other Grand Slam quarter-final came in 2008 when he lost to Federer at the US Open.

He trails last-eight opponent Marin Cilic 2-0 but he has been in fine form on grass this summer, winning the title at 's-Hertogenbosch and reaching the semi-finals at Queen's where he lost to Cilic.

Cilic, the 2014 US Open champion, is in the quarter-finals for a fourth successive year.