The Scottish giants will host Milan in the first-leg of the Champions League's round of 16 in Glasgow and Nakamura believes the Rossoneri poses a threat despite their recent dip in form.
"They are a big club with international players in every position and they've won the league many times," Nakamura told Japanese television.
"I played against them many times when I was at Reggina and they seemed almost impossible to beat.
"They are very strong and have many intelligent players who know their football.
The Japanese set-piece specialist believes that Milan's danger is most likely to come from Italian playmaker Andrea Pirlo.
"I think the key to Milan is Pirlo," said the Japanese international.
"He positions himself in front of the back four and makes accurate passes - he can turn the tide with one play.
"They are very good at that kind of counter-attacking. Milan will go on if we can't stop Pirlo.
Nakamura marked out the quality of other Milan stars including Kaka, Gennaro Gattuso and goalkeeper Dida who is most likely to miss the game through injury.
"Gattuso is like a fighting dog. Kaka is fast and tough. Dida, I think, is the best goalkeeper in the world."