The French star joined Arsenal in a £5million deal on Friday.
Diarra said: “I needed to play and get more time on the pitch and I don’t think it would be possible at Chelsea. That’s the main reason why I left.
“At Chelsea, we had Michael Ballack, Frank Lampard, Claude Makelele and Michael Essien in midfield.
“I know it will be tough to make it at Arsenal as well.
“I have no guarantee from Arsene Wenger I will play all the time but I am sure that it will be OK.
“I know I will play big matches in the league and even in the Champions League.”
