The DC United coach was stunned by the show of arrogance from Mbappe during last week's victory over Montpellier. The Frenchman clashed with Neymar over the taking of a penalty and also shoved Leo Messi in the process.
Interviewed by Depar Sports, Rooney said: "A 23-year-old player who shoves Messi ... I've never seen a bigger ego in my life!
"Someone should remind Mbappé that when Messi was 23 he had already won four Ballon d'Ors."