"When they come back from South Africa there is an opportunity to talk again.
"I fully trust Sir Alex's word on that and when they come back from South Africa I will be putting a call in. There is always a possibility."
Campbell is likely to command a fee of around £5million and other clubs, including Aston Villa, have also been linked with the youngster.
It is unclear whether United would sell but such a priority is he that Brown would also be interested in bringing the player back to the KC Stadium on another loan deal.
"He is very, very important to me, and that we get the right quality strikers in," Brown added.
"It is difficult. There are one or two strikers out there we have earmarked as priority but if Fraizer Campbell became available we would certainly be interested in taking him, either permanent or on loan."