Mannone's place in the Sunderland side is believed to be under threat due to his recent displays, and the spotlight was on the Italian once again last weekend as he made a vital error in the 2-0 defeat to Arsenal.
However, his former teammate Flamini is certain that he can become a dependable option for Black Cats boss Gus Poyet as the speculation surrounding his place in the team continues.
"He is a friend of mine," the Frenchman is quoted as saying by the Northern Echo. "It was a difficult time for him. The confidence in the Sunderland team was not high.
"I played with him at Arsenal. He is a great keeper and a great guy. I felt for him, but he will bounce back."