Joshua has suffered consecutive defeats for the first time in his professional career after once again falling short against Oleksandr Usyk in the summer, even though he did produce an improved performace in the the rematch in Saudi Arabia.
It has left the 32-year-old in the pack behind the division’s very elite, though there is still the potential of an immediate return through a bout against Tyson Fury in December as talks continue over a massive all-British clash.
Joshua is expected to fight before the end of the year regardless of whether terms can be agreed with Fury as he looks to get his career back on track with a first win in almost two years, with promoter Eddie Hearn stating he wants the heavyweight to be far more active now he is free from any mandatory obligations.
The second defeat to Usyk in August was Joshua’s first under new trainer Robert Garcia, and Wilder believes the priority going forward should be on improving his ability to keep up the pace for the full 12 rounds.
“I just think Joshua was very cautious in what he did as far as exchanging punches [with Usyk],” Wilder told SkySports.
“I always forever said it, as I see it he has a big stamina problem.
“I think if he can correct that, I think you will see a different Joshua. You won’t see one that’s so hesitant to throw punches and do things especially when he had Usyk, was close to getting him out of there.
“I think he was just a little fearful of running out of gas too quick and too fast and he held back a little bit.”
He added: “It’s not over for him unless he says it is.”
Wilder returns to the ring in October against Robert Helenius, almost exactly 12 months on from his defeat in a trilogy fight against Tyson Fury.
The American has expressed an interest in a possible fourth fight between the pair in the future, while Oleksandr Usyk, holder of the WBO, WBA and IBF belts, has said he would be keen on fighting Wilder, should he get past Helenius, early next year.
“I heard about the Usyk situation and he’s going to be [at the Helenius fight],” Wilder said.
“I hold Usyk to be a man of his word. If Usyk’s saying he wants to give me an opportunity for the titles then that’s what I’m holding his word to.”