Irwin has watched Kagawa in action for Borussia Dortmund and believes it won't take long for the Japanese midfielder to become a crowd favourite at Old Trafford.
Irwin told ManUtd.com: "He's the type of player that most United fans felt we needed, an attacking, all-action player.
"I saw him playing a couple of matches for Borussia Dortmund and he seemed a very talented player, lively with great technique. I know he was highly rated in Germany.
"I think he'll be a great signing and fans should be excited by the prospect of him playing for us because he can run with the ball, create chances and score goals. He's just what we need."