According to the Daily Mail, the South African striker received the pecuniary punishment 'after he fell behind their deadline to lose weight" and 'the fines built up after he missed a series of deadlines in a gruelling fitness programme'.
In pre-season Hammers chairperson David Sullivan told the tabloid McCarthy's body fat ratio had soared to 24.2%, with the optimum weight for a professional athlete between 5-12%.
Since joining the London club from Blackburn Rovers in February 2010, McCarthy has done little to justify his £2.5m price tag and £40 000 per week wages.
But on Monday Avram Grant told the Daily Telegraph he expects the former Ajax Amsterdam and Porto marksman to play an important role this season.
"He's lost eight kilos and is a very good player and I'm sure he will help us - and that's what's important," said Grant.
The 32-year-old's weight is said to be around 85kg now which is within the target range set by West Ham's medical team.
With the Hammers currently bottom of the English Premiership and in desperate need of goals, Grant is expected to recall McCarthy to his first-team squad to bolster his goal-shy attack.