Muntari made his debut at Stoke after joining the Black Cats on loan from Inter Milan.
Gyan said: “I first played with him eight years ago. We didn’t know each other as schoolboys but I played with him for the national team.
“Before coming here I knew what he was going to do. Every time he’s on the ball I know what he’s going to do. I just took advantage of that.
“I’m disappointed with the result. We were in control of the game, especially the second half, but they came back strongly. They fought hard.
“I think we were better than them but they beat us with their quality.”