The BBC pundit disagrees with the Aston Villa manager over his treatment of the young midfielder.
Grealish was recently pictured on a night out and Remi Garde has since acted by dropping and disciplining the 20-year-old.
However, Sinclair feels punishing the midfielder is harsh and believes he hasn't really done anything wrong - a view some Aston Villa fans certainly seem to agree with.
Indeed, on social media, the pundit responded to a follower by defending Grealish and suggesting he simply did something anyone else would do. Many have emphasised the fact there was no match the following day, meaning the youngster technically didn't break any rules.
Sinclair did go on to admit the need for man management but feels Garde's methods aren't what's needed in this case.
The pundit clearly wants Aston Villa to embrace a more welcoming approach with the 20-year-old.
Do you agree with Sinclair or is Garde right to be firm with his players?
Aston Villa travel to Southampton for their next Premier League clash. If there's anyone other than Villa who are low on confidence at the moment, it's the Saints.