The South African striker scored two penalties in the 4-1 win against Bolton Wanderers on Sunday and has opened talks over extending his present terms, which run until 2010.
After becoming an instant hit with Rovers, McCarthy's form has been less impressive this time around after being linked with a move to Chelsea in the summer.
Nevertheless, he remains an important part of Hughes's plans and discussions are underway to extend his contract.
"The talks are still ongoing," said Hughes. "We spoke to his agent this week so hopefully something will be resolved.
"There isn't really a timescale on it."