The French left-back has struggled with injury issues since arriving at the Citizens in 2017.
But he is always active on social media, sometimes annoying his manager Pep Guardiola with his obsession. And Dunne agrees.
He told grandnational.org.uk: "[Paul] Pogba was on social media all the time earlier this season and wasn't playing well.
"Like Mendy, it's great having a laugh but make sure you're contributing to the success of the club and not just feeding off of it.
"Make sure you're doing your job before you're posting anything.
"It's a bit of distraction, and something the manager could do without."