The Scottish international has reportedly attracted interest from Liverpool after scoring five times in his last six league games.
However McCarthy said Tuesday Fletcher would remain a Wolves player and is expected to recover from an ankle knock in time for this weekend's meeting with Spurs.
"There is not a chance of Fletch leaving. If people call, I'd tell them no. He's too valuable for us," McCarthy said.
"As regards his fitness, he's got a sore ankle. He rocked it in the FA Cup tie at Birmingham. He didn't train on Monday but he will be okay."