Andy Murray Photo: Kirsty Wigglesworth/AP

Defending champion Andy Murray will retain his world number one 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 world number one 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 won't 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 who has made the last-eight despite lingering worries over a hip injury.

"When he's standing up on the baseline, hitting forehands, dictating, he's a very dangerous player."

Querrey made the quarter-finals in 2016 where he lost in four sets to eventual runner-up Milos Raonic.

Novak Djokovic Photo: Alastair Grant/AP

He has needed two successive five-set matches to get to the last eight, seeing off French 12th seed Jo-Wilfried Tsonga and Kevin Anderson.

Querrey has also sent down 99 aces, just three behind tournament leader Gilles Muller, the conqueror of Rafael Nadal.

The world number 28 will also attempt to become the first American in the semi-finals since Andy Roddick finished runner-up in 2009.

With Nadal out of the picture, Murray will be assured of remaining as world number one with victory on Wednesday.

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 in what proved to be Federer's last match of the season.

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

"I've not had the most toughest matches. 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.

Raonic, runner-up to Murray last year, is bidding to make the semi-finals for the third time.

However, while Federer has not dropped a set, the big Canadian needed five sets to see off highly-rated German Alexander Zverev in the last-16.

Roger Federer Photo: Kirsty Wigglesworth/AP

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.

Second seeded Djokovic needed a medical timeout to treat a long-standing right shoulder injury in his last-16 clash with Adrian Mannarino.

He also claimed a hole had opened up on the service line on the Centre Court.

"The courts are not great this year - I've played on better courts," said Djokovic.

Berdych hasn't 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 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.

He has lost in the last-eight in each of the last three years - falling to Djokovic in 2014 and 2015, and to Federer in five-sets last year despite holding a 2-0 lead.

AFP