Birmingham's Frankie Gavin says he will radically alter his diet and fight at light-welterweight after failing to impress against Curtis Woodhouse.
Gavin, 25, won a split decision as he defended his WBO Inter-Continental welterweight title in Liverpool.
"I'm going to have to change something drastically," Gavin told BBC WM.
"I'm going to have to change my diet and get down to ten stone. Ten (stone) seven completely knocked me out, I don't feel as quick."
The win took Gavin's unbeaten record to 11 wins but Britain's former world amateur champion knows he was far from his best.
"I just felt terrible. I give it a five or six-out-of-ten performance," Gavin added.
"I'm not boxing at where I should be so I'm going to have to change a little bit."
Of his 11 fights so far, nine have been at light-welterweight and Gavin is convinced that is where he should return, after struggling in his last two bouts at the higher weight against Young Mutley and Woodhouse.
"'I'm looking a million dollars in the gym, it's just in my last two fights in the ring I haven't," Gavin said.
"When I'm throwing I'm landing but I'm just not throwing enough."
Gavin is also concerned that his below-par performance will mean people will start doubting his ability to reach the top.
"I'm better than that so I'm going to have to come out and prove it I've got a lot of doubters now and I've got to prove them wrong.
"I'm going to have two weeks offs and then straight back in. I'm going to be back in September."