Joshua, 35, suffered a tough loss to Daniel Dubois at Wembley Stadium in September. The fight for the IBF heavyweight title ended in the fifth round with Joshua hitting the canvas four times before the stoppage.
Benn, now 60, believes Joshua can bounce back. He told reporters:
"I still believe that Anthony can come back from that. But he needs some mongrel put in him. I know he's got it in him."
The boxing veteran expressed his desire to work with Joshua in the gym:
"I'd love to be in the gym with him. Not saying he's lacking encouragement, but you have to get that mongrel inside you that I know is in you and I still think that he can turn it around."
Joshua's team has ruled out an immediate rematch with Dubois. They've said AJ needs more time to recover from injuries he got in the fight.
Eddie Hearn, Joshua's promoter, hasn't completely closed the door on a second bout with Dubois. He's waiting to see what happens in the December 21 rematch between Oleksandr Usyk and Tyson Fury before making any decisions.
Joshua has lost twice to Usyk in the past. Fans have long hoped for a big all-British showdown between Joshua and Fury, but it hasn't happened yet.
Benn thinks Joshua should focus on getting revenge against Dubois before looking at other opponents:
"I'm not knocking the training or anything, but you've got to bring that hunger. But I don't think he should go anywhere else, but fighting Dubois."
Meanwhile, Dubois is set to fight on February 22, but his opponent isn't confirmed yet. Joseph Parker and Zhilei Zhang are possible contenders.