The 24-year-old will reportedly be offered a four-year deal, with Harry Redknapp eyeing him as Rob Green's long-term successor.
McCarthy will also be expected to challenge Green for a role in the starting XI, as Redknapp looks to create competition for a place between the posts.
Meanwhile, the Rs could also bring a new defender to Loftus Road in Gremio centre-back Gressan.
"A proposal was made [by QPR] that matches what we expected. But we are still waiting the club to make an official offer,” the 21-year-old's agent Marcelo Lipatin told Globo Esporte.
"But the way things are going, [the transfer] will probably happen, all parties have reached an agreement."
The west London side beat their local rivals in the Capital One Cup thanks to McCormack's winner and Magath insists the win will build confidence for both the £11m striker and the rest of the squad.
"I am very pleased for him because that goal will give him confidence and the win will give us confidence for the future," Magath told reporters.
"We dominated parts of the game and it was a very good performance which will give us confidence for the future. I am happy with the result, our first win of the season, and it was very important for us."
McCormack, meanwhile, praised Magath's training methods and has backed the German to come through Fulham's tough spell.
"His fitness is different to any fitness work I have done in the past," he told reporters.
"He has been getting a lot of criticism but he will take that on the chin because he is the manager of a big football club, that is part and parcel of it."