Flamini has faced United several times during his time at Arsenal.
He said: “I played for four years in England and it was a formative and fantastic experience. Apart from playing against Portsmouth I haven’t played against an English club since then.
“I have told my team-mates to expect a tough, physical game. It will be a battle for us.
“Whoever wins the battle in midfield will win the tie. I have had many battles with United over the years. It will be amazing to play against them.”
He added: “I still have many friends at Arsenal and I talk to them a lot. Especially Cesc Fabregas who is a very special player. I would love to play against him – and them – in the final in Madrid.
“When I left it was a great opportunity to play for one of the biggest teams in the world.
“But I will never forget my time with Arsenal. Arsene Wenger developed me as a player and I will always be in his debt.
“Arsenal are in my heart – and will be in my heart for ever. But I’m very happy at Milan now.”