Wimbledon 2017: Roger Federer & Novak Djokovic through after opponents quit

Roger Federer and Novak Djokovic said Wimbledon should consider rule changes after both their first-round opponents retired with injuries.

Third seed Federer led 6-3 3-0 when Ukrainian Alexandr Dolgopolov quit with an ankle injury after 43 minutes.

Second seed Djokovic progressed after a calf injury saw Martin Klizan pull out after 40 minutes at 6-2 2-0 down.

"We had a joke in the locker room saying we should maybe play a practice set on Centre Court," said Djokovic.

Both Klizan and Dolgopolov have struggled with injuries recently and their retirements were among a total of eight - seven in the men's draw and one in the women's - over the first two days of the Championships.

The men's tour, the ATP, introduced a rule at the start of 2017 that means a player can retire before a first-round match and retain their prize money.

A lucky loser then gets the place and money earned from qualifying, plus any further prize money accrued from the second round onwards.

The rule is not in place at the four Grand Slam tournaments.

"Maybe it should be addressed," said Djokovic.

"I think the new rule that the ATP has reinforced allows players who have made it to the Grand Slam main draw to get what they deserve, but at the other hand allow someone else to play if they can.

"I support that kind of rule."

The 15,000 spectators were at least cheered by the news that former world number one Caroline Wozniacki and Timea Babos would make a surprise appearance on Centre Court to bolster the schedule.

Three-time champion John McEnroe said on BBC Sport: "I do think when you saw Klizan, he clearly wasn't ready or able to play from the very beginning.

"They've got to figure out some kind of rule change where, I suggest, they give him half the first-round prize money and bring someone else in who is at least fit and can go out 110%.

"It's not a good look for our sport when you have to sit and watch that on Centre Court.

"For someone like Klizan, that £35,000 [first-round prize money] really matters and he's reluctant to give that up.

"That's where you need to get the powers-that-be at Wimbledon, the ATP, all the people involved in our sport, even a coach to speak to Martin and make him understand that in the best interests of the sport, and for himself - he's risking a worse injury.

"This isn't something that just cropped up, he's had issues with this for a few months, so he's got to get this sorted out."