The rumor was doing the rounds last year that Superman would be making an appearance in the Green Lantern movie. Even though these rumors were brought to us by the film's co-screenwriter Marc Guggenheim(the git!), it turns out it was all a load of bay.
MTV asked Campbell about the possibility of GL flying into Supes at some point, to which he said.
"No, that won't happen. None of the other DC characters will appear in the film."
I think it was kind of obvious this wasn't going to happen after news that another Superman movie was way off for Warner Bros and DC. Still, disappointing.