Bruce Kamau joins Melbourne City after Adelaide departure

Bruce Kamau says it's with a heavy heart that he leaves Adelaide United for A-League rivals Melbourne City.

The 21-year-old Kenyan-born winger confirmed a move on Friday, just five days after opening the scoring for United in the Grand Final.

The adopted home-town hero was a firm fan-favourite in Adelaide, and said leaving United's supporters behind was the toughest thing about moving east.

But Kamau said a need to get out of his comfort zone to "go to the next level" of his career drove his decision to move to City.

"It's a hard decision to leave the club, especially after such a good year and the way we turned it round," he told AAP.

"I'm from Adelaide. I grew up here. My family is here.

"The direction City is taking is fantastic. They've got a good vision.

"It's a great opportunity and hopefully if I do well it will present other opportunity with the group."

Kamau said Guillermo Amor and his coaching predecessor Josep Gombau were "great mentors," giving his fellow championship-winners the most praise.

"You have been the most inspiring and motivating individuals [and] your impact will live with me forever," he said.

"You exemplify what a team truly is, together we each achieved more. We had an incredible season. I will be forever indebted to each of you."

Kamau is already popular with City fans, having scored a late winner against arch-rivals Melbourne Victory at AAMI Park in February.

He has signed a two-year deal with City, with new coach John van 't Schip confident of seeing great progress over that time.

"He is still young, has shown positive signs and he is a player we see as having great potential," van 't Schip said.