City's Head of Communications Paul Tyrrell said yesterday: "We can confirm that a player has been suspended until the end of the season, pending an internal investigation into a training incident at the Carrington complex."
Barton is believed to have punched fellow midfielder Ousmane Dabo at training on Tuesday, and although the club is yet to name the culprit, Barton's agent Willie McKay told BBC Sport: "As far as I've heard, Joey was defending himself. But because it is Joey it makes headlines.
"It happens on training grounds all over the country, from Chelsea to Yeovil," McKay added.
Amongst the things that Barton criticised after the Watford game was the club's summer signings, one of which was Dabo, who is thought to have been taken to hospital with mouth injuries.