The three-time winner joined in the growing criticism of the playing surface following his third-round victory over Ernests Gulbis on Centre Court.
Defending champion Andy Murray claimed on Friday that the courts are not in as good a state as previous years, while earlier in the week French player Kristina Mladenovic branded Court 18 “dangerous”.
That criticism, along with the serious knee injury suffered by American Bethanie Mattek-Sands – which is thought not to have been caused by the surface – have made it a trying first week for Wimbledon chiefs.
Head groundsman Neil Stubley staunchly defended the condition of the courts on Friday, when saying: “We set them up to the exact standard we’ve done in many previous years.”
However, Djokovic said: “In the first two matches I didn’t see any significant difference, but I was hearing a lot of comments from the other players.
“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 the baseline area.
“I haven’t had that kind of experience before in Wimbledon, to be honest. I mean, the courts are always perfect here.
“But I’m sure that the groundsmen will try to do everything possible to make it playable as much as they can in the second week.
“I’m sure they know what they’re doing. They know their job the best in the world. But you can see that there is a slight difference in the quality of the grass. This year seems like it’s a bit softer.”
Seven-time champion Federer was on Centre Court straight after Djokovic, beating Mischa Zverev in straight sets.
The Swiss, competing at his 19th Wimbledon, does not feel the courts are any different from previous years but fears other players may have concerns about getting injured.
“I feel it’s the same,” he said. “When it does get very hot, the sun beats down on the court for the entire day, I do feel the courts get a tad slippery.
“There’s all this dead grass, in the middle in particular, because it’s not attached anymore. I feel like that’s sort of the slippery place sometimes.
“But I didn’t feel like it was unsafe. Maybe you don’t want players to feel that way because the moment you become scared of moving properly, it’s really difficult to play. The last thing we want to see is horrible injuries.
“I think it’s going to be interesting to see what they’re going to do with the courts (on Sunday’s rest day). I would like to find out what the greenkeepers are going to do.
In the women’s draw, top seed Angelique Kerber staged a splendid recovery to see off American Shelby Rogers 4-6 7-6(2) 6-4 in the third round.
Kerber will face 2015 finalist Garbine Muguruza in the last 16 after the Spaniard eased into the second week of the championships without dropping a set.
Poland’s ninth seed Agnieszka Radwanska recovered to beat injury-troubled Swiss Timea Bacsinszky 3-6 6-4 6-1 to set up a last 16 clash with Russian eighth seed Svetlana Kuznetsova.
