"It's a racing certainty that Andy will be going to Cardiff," said McCarthy.
"Andy has been fabulous here both for me and this football club. It's a good move for him to go to Cardiff and good luck to him.
"He wants to play football and doesn't want to be fourth in line here which I can fully understand.
"It was my decision to let him go but he goes with our best wishes and warmest regards."
Keogh, 24, is a Republic of Ireland international. He came off the bench in Ireland's recent friendly defeat agaisnt Artgentina. He has scored 19 goals for Wolves in 79 League starts.