The former Chelsea midfielder penned an 18 month contract with the Rossoneri this week.
"Essien and I have been friends for 12 years," he told Milan Channel. "We have often shared a room together in the national team.
"He works a lot, speaks little and sleeps a lot as well!
"I'll help him adapt to life here quickly, and I'm sure he'll be making a crucial contribution soon."
Muntari then went on to comment on Clarence Seedorf's impact since arriving as Coach.
"I'm sure it's not easy going from player to Coach, but the important thing is that we have such a good group here.
"Things are going well but we have to keep on working hard.
"If we keep on helping each other then I'm sure we can do well."
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