Strootman joined OM yesterday in a surprise move amid claims he was sold against his will.
But the Dutchman stated: “It's a great club and a great challenge.
“I'm really happy to be here. I talked to the Coach, the President and the sporting director. This club wants to win and I want to help them achieve their goals. I'm happy to be here.
“(Rudi) Garcia is a special person for me, he took me to Roma and he wanted me again. I spoke to him about the tactical system and everything else, I hope he's as happy with me as he was in previous years.
“Did I leave Roma because of Nzonzi? It's not like if a player comes in I leave, they've signed a lot of players. It's normal, it's a great club and they were right to sign them, competition is normal.
“It was right to leave, the time had come, I'd been in Rome for five years. [Juventus' Medhi] Benatia told me positive things about this club."