The veteran striker is one of the few players on Cardiff's books with Premier League experience.
Hartson told BBC Sport: "I'm working now with Craig with the national team alongside [Wales manager] Chris Coleman and he's a great influence around the place.
"He will be able to help those young players who have never played at this level before.
"Craig's obviously had a wonderful career at West Ham, [Man] City and Liverpool. He's vastly experienced.
"I'm sure Craig will want to play every week - I know what the boy is like. But I think Malky will have to put the reins on him at times and hold him back slightly.
"He's the other side of 33 now and you wouldn't expect him to play every single game, but he's in great condition and looks after himself."