(CNN) Be it the lack of a roof several years ago or its strict clothing policy, there always seems to be controversy at Wimbledon .

This year the grass at what is considered to be tennis' most prestigious tournament is coming under scrutiny, especially after American Bethanie Mattek-Sands badly injured her knee in a fall while approaching the net in a second-round clash on Thursday against Sorana Cirstea.

Those questioning the quality of the lawns aren't limited to competitors who have rarely played on the grass but include former Wimbledon champions, although Mattek-Sands' description of her injury in a Facebook live video suggested the grass wasn't to blame.

No play on Sunday, as per tournament tradition, may have given the beleaguered grass a rest but that was tempered by a hectic Monday, which saw every player remaining in singles, men's doubles and women's doubles, on the schedule.

Novak Djokovic picks up a piece of loose turf from Centre Court during his third round match with Ernests Gulbis on Saturday.

"The first two matches I didn't see any significant difference," three-time Wimbledon winner Novak Djokovic told reporters Saturday, when asked to compare the grass to years past. "But I was hearing a lot of comments from other players. They were complaining, especially on the outside courts.

"But today I could see there is a difference in the grass, in the turf itself. It was a bit softer, I would say, especially around a couple of feet inside and outside, around the baseline area.

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"I haven't had that kind of experience before at Wimbledon. I mean, the courts are always perfect here."

When the Serb referred to his fellow pros "complaining" about conditions on outer courts, he might have been referring to Kristina Mladenovic for one.

On the same day Mattek-Sands sustained her terrible mishap, the outspoken 12th seed slipped at least three times on Court 18 -- the same arena where John Isner outlasted Nicolas Mahut in the longest match in tennis history in 2010 -- in a defeat to American Alison Riske.

Bethanie Mattek-Sands receives treatment from paramedics following her fall last Thursday.

According to Mladenovic, who slightly injured her knee and ankle, holes were visible on court.

'There's no grass'

At one stage in the first set, play stopped as Mladenovic and Riske discussed the state of the turf with supervisor Pam Whytcross.

In a briefing with reporters Thursday, Riske -- who generally likes to compete on grass, the most specialized of tennis' three main surfaces -- likened a part of the court to "ice."

"There's no grass," Mladenovic told reporters. "I don't know how to describe it. It's not even clay. It's not flat.

"It makes it, of course, tough to put your strong footwork. You kind of have to run light and be careful, I don't know, not to push or press too much, too hard, which is strange to play on.

Kristina Mladenovic suffered several slips during her match against Alison Riske.

"I'm just honestly very happy and blessed that I didn't injure myself that much."

This isn't the first time the grass at Wimbledon has drawn the ire of competitors.

In 2013, twice grand slam winner Victoria Azarenka slipped on the grass in a first-round victory, injured her knee and withdrew ahead of her second-round contest. And Maria Sharapova described the court as "dangerous" in an upset loss to Michelle Larcher de Brito, having taken a tumble three times.

That year, more rain than usual in England in May, little sun during the first four days of Wimbledon and humidity, noted the New York Times , perhaps meant the courts hadn't sufficiently dried.

But this year, the issue could stem from too much heat and a lack of rain.

Most parts of England experienced a heat wave a week-and-a-half prior to Wimbledon, with several days of warmer than usual temperatures following last week. Meanwhile, rain only briefly surfaced one day of the first week, last Monday.

Brown, or dead, worn-out grass that usually results deep in the second week was thus an earlier than normal visitor.

Federer weighs in

"It changes color," Roger Federer, chasing an eighth Wimbledon title, told reporters Thursday. "And that bit can be slippery. So it makes moving hard.

"I don't know if that's tougher than just green grass, when it can slip out of nowhere, in my opinion. At least with the other one at least you know it's a bit different. I mean, it's always been like this.

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"Now, is it more this time around? Possibly, because it's been extremely hot today and yesterday. So that's why maybe -- that's what we are hearing.

"It's not a good sign, and you should always take the players' opinion seriously, especially when both say it."

In an unusual move, Wimbledon made head groundsman Neil Stubley available for an interview with England's press agency, PA , on Saturday, with his comments then circulated to reporters.

He denied that the courts this year were more slippery than usual.

"More slippery? I don't know if there's been more slips this year or there's just been a couple of high-profile ones," he said. "I'm not sure.

"Well, obviously we listen to players," he added, "because their feedback is important. But the data shows to us those courts that are in question are within range of the other courts, and they are within the range of previous years.

"That's all we can work to, is the data that we feel is best for the health of the courts."

Stubley insisted that the courts would hold up through the second week, which began Monday.

"Absolutely. Absolutely," he said. "There's not a doubt in our minds that the courts will not be as good as they need to be for the end of the Championships."