The 31-year-old has scored 10 goals in 16 games to help ignite Town's mini revival but will returns to parent club QPR after Tuesday's game against Brighton.
"He'll go back and we'll see what happens after that," said McCarthy. "I think Harry Redknapp, in his position, will want to have a look at him. It was always the case that he was going to go back.
"We are trying to do a deal to keep him and hopefully we can. Fingers crossed, we'll see.
"We're speaking to his agent, I've spoken to DJ and we've offered him permanent deal effectively. There's a permanent deal there for him if that's what he wants to do.
"He loves it here though and I think he'd be happy to stay provided we can do a deal with his agent and QPR. There's a lot there to be dealt with.
"I'm conscious that we can't leave things too late in the window. I am actively looking and speaking to people about other players."