Messing meanwhile uploaded a post calling for fans to vote for Will & Grace for the Emmys but failed to tag Mullally.
Their co-stars Eric McCormack and Sean Hayes still follow both women and they follow them back.
It follows the surprising news that the rebooted Will & Grace would not be returning for another season despite decent ratings.
Messing was cast as interior designer Grace Adler when they show began in 2006.
She lived with her gay best friend, Will Truman, with Mullally playing her alcoholic assistant, Karen Walker.
The show ran for eight seasons before being rebooted in 2017.
Fans were left devastated that Messing and Mullally may longer be friends.