McCarthy believes Ipswich would be Campbell's first choice if he was to leave QPR, but he is aware his form at Portman Road could increase competition for his services.
"They [other clubs] will have all noticed DJ scoring goals here but there is nothing we can do about that," McCarthy told the club's official website.
"All we can do is try and do a deal with him. He wants to stay long term at a club and I think this club would be his first choice, with things starting to go better.
"But there are a lot of mitigating circumstances that can change that situation. Let's just wait and see."