Lennox Lewis feels David Haye may struggle against Anthony Joshua due to his lack of ring-time over the past four years.
Former WBA heavyweight champion Haye is due to fight Arnold Gjergjaj next month, his second outing since ending a three-and-a-half year hiatus in January with a one-round stoppage of Mark de Mori.
Haye has talked up a future bout against newly-crowned IBF champion Joshua, but heavyweight legend Lewis has warned that his experience could count for nothing after spending so long nursing injuries.
He tweeted: "I think people are imagining the peak David Haye, so was I, but considering his inactivity over last four years, and his choice of opponents, there are questions.
"It's the age old argument of youth and strength pitted against experience and skills. Haye's inactivity also leaves question marks."
Haye won the WBA title from Nikolai Valuev seven years ago before failing to unify the heavyweight belts against Wladimir Klitschko in 2011. He fought just once more, beating Dereck Chisora, before retiring due to a shoulder problem which has now been rectified.
After Joshua knocked out Charles Martin in two rounds to become IBF champion last weekend, Haye immediately told Sky Sports about a desire to pit his wits against the new title-holder.
"Joshua wouldn't let his hands go with me because I'd unsettle him and drag him out of his comfort zone," Haye said.
"You have to put him on the shelf from really early on. If I stood on the outside and went jab for jab, he's got longer arms than me.
"I'd want it pretty soon. I don't believe there's anybody out there he could learn against."