Former world super-middleweight champion Richie Woodhall is urging Audley Harrison to be more ruthless in the ring.
Harrison insists he is beginning to lose his "nice guy" tag following his ill-tempered points win over Dominic Negus.
"To gain any credibility, Audley has got to start knocking out guys like Negus," said Woodhall, who was commentating on Wednesday's fight for the BBC.
"Frank Bruno, Lennox Lewis and Mike Tyson were knocking people out left, right and centre when they were at the same stage of their careers, but Audley has a problem putting people away.
"You have got to question his punching power in that respect.
"Negus was tailor-made for Audley. He was a short, pumped-up cruiserweight who liked coming forward, but for some reason Audley couldn't knock him out.
"Don't get me wrong, I would not like to be on the end of one of his punches, but he is not a devastating puncher."
Woodhall thinks Harrison will struggle to win one of the respected world titles.
But the former Telford fighter, who held the WBC version of the super-middleweight title, says his 30-year-old compatriot still has time on his side.
"All this talk about him being too old is rubbish," said Woodhall.
"Boxers in the heavyweight division can go on forever if they keep themselves in good shape.
"Physically, it should not be a problem for Audley. My worry is that he may not be mentally up to it. Will he want to keep on going?"
In the meantime, Woodhall says Harrison must be patient.
"He is only an average six-round fighter," said the former Olympic bronze medallist and Commonwealth Games champion.
"Yes, Wednesday night was an improvement, but he can't even contemplate going 10 or 12 rounds yet. It will be another two years before that happens."