The Scotland international has proved an excellent signing since joining from Burnley in 2010 and has scored nine league goals from 16 appearances this term.
Fletcher scored in recent draws with Arsenal and Bolton along with netting against high-flying Tottenham last time out.
McCarthy has already affirmed the striker is 'not for sale' and the Molineux boss is delighted with his contribution of late.
"Fletcher is proving to be one of the best in the league at the moment," explained McCarthy. "I'm delighted with him.
"Steve's a talented player - he scores goals and makes it hard for defenders by closing people down."