The Swansea smasher claims he is suffering "the worst year of my life" after two defeats left his career in tatters.
His WBO world title was snatched when David Haye stopped him inside two rounds in March 2008, and just three months ago he was the victim of a huge upset losing in nine rounds to Ola Afolabi.
Maccarinelli has the chance to wipe out the bad memories when he meets Russian southpaw Lebedev for the vacant WBO inter-continental cruiserweight title at Manchester's MEN Arena on July 18.
The 28-year-old quit Enzo Calzaghe's camp after losing to Afolabi and is now training in the north west of England with unknown coach Karl Ince.
Maccarinelli said: "I've had a terrible year - the worst of my life, boxing or otherwise. If I don't win this fight against Lebedev, I won't be boxing again. I can't go back to British title level.

"My back is up against the wall, but right now I've never felt so ferocious before a fight. I'm embarrassed by my performance against Afolabi and I'm hurting inside over that defeat. I must avenge it."
Maccarinelli believes he was neglected before that shocker by Calzaghe, who was pre-occupied with his son Joe's court case against promoter Frank Warren.
He said: "I did little strength and conditioning and no sparring at all for the Afolabi fight, and at the end of the first round and I was completely exhausted."

The switch to Ince has meant leaving pregnant wife Eloise and their four children at home while he prepares for the make-or-break fight 235 miles away in Bolton.
He makes a 10-hour round trip each weekend for a family visit but added: "Being away from my family five or six days a week has made me stronger and I'm enjoying training.
"It's difficult, I'm a family man and I miss my kids and wife, but I'm doing this for them. If I can get back to where I was I can give them a good life."
Ince, 46, a former journeyman middleweight was in Maccarinelli's corner assisting Calzaghe when he lost to Afolabi.
Big Mac added: "With Karl it's different, I realise the importance of giving your body a rest and not drilling yourself into the ground."
This article has 1 comment
Defeat Dennis Lebedev and have a rematch with David Haye. I think Enzo CAN beat David Haye.
By Toby. Posted July 11 2009 at 10:53 PM.