Witter has won 36 of his 40 fights, but lost his last bout
Junior Witter believes he has come back a better boxer after losing his WBC light-welterweight belt.
The 34-year-old returns to the ring on Saturday for the first time since his defeat by Timothy Bradley in May.
"I'm fitter and stronger and I'm still on top, which I'll prove," the Yorkshireman told BBC Radio Sheffield.
"I'm hungrier than ever before. It's not good not having a belt, I don't feel right without a belt. I want my title back."
For the first time since his defeat in May the Sheffield-based boxer has admitted he should not have taken on Bradley.
Witter's father Walter was diagnosed with lung cancer and underwent his first course of chemotherapy just two days before the then-champion was due to defend his crown.
I have to go in to the ring on Saturday and win obviously. I will be back, I will be on top. I am the man and I will be the man. Keep watching
Junior Witter
Walter has now made a steady recovery and is expected to be ringside at London's York Hall to watch his son's 10-round encounter with Argentina's Victor Castro.
Bradford-born Witter explained: "I shouldn't have got in the ring.
"I peaked a couple of weeks earlier and had a lot of other mental pressure on me outside the fight.
"A lot of people who knew the situation told me to pull out.
"But I had this thing that I'd said I'd do the fight so was going to do it. I should have pulled out."
Castro, 33, is the 10th boxer to be lined up as Witter's opponent for Saturday's fight and has won 29 of his 33 fights.
However Witter is confident of victory and hopes to move on to a title fight as soon as possible.
"I expect to have a title fight by the summer, that's what I'm hoping for.
"I guess we'll just have to wait and see how it pans out.
"I have to go in to the ring on Saturday and win obviously, and that's the main goal to achieve.
"I will be back, I will be on top. I am the man and I will be the man. Keep watching."
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