The British fighter lost his world title belts to Usyk after losing their bout last weekend, which dealt a major blow to his hopes of unifying the world titles against Tyson Fury, but Klitschko suggested that the fighter can bounce back and used his own career as an example.
Klitschko, who was beaten by AJ in 2017, told Sky Sports: "We have seen AJ challenged.
"I remember my time. I lost two fights within [13 months in 2003 and 2004].
"To bounce back? To eventually become one of the longest-reigning champions?
"AJ can still have his time, absolutely. It is all about how to overcome the challenge."
The Ukrainian legend was also full of praise for his compatriot Usyk, who produced an outstanding performance to claim the title.
Klitschko said: "Usyk made history.
"Since 2012, I watched Usyk winning his gold and I watched AJ winning his gold.
"Usyk has been undefeated for such a long time, winning all the titles as a cruiserweight and now with the heavyweights.
"This man is something special."
Joshua also got some advice from Fury, who urged him to recognise that the sport of boxing is not "rocket science".
The fighter said: "There are no secrets, no rocket science, to boxing.
"Fighters today make it technical. This is just two men punching each other for 12 rounds or less."