The singer was seen being forcibly removed from The Villa in Essex by bouncers in the early hours of Sunday morning with a bloody face.
Jay apparently got into a fight with customers after being accused of stealing drinks from a table.
“He pushed back to try to get them off him, so the security thwacked him. He was knocked clean to the floor, and was dragged from the venue."
The 23-year-old was at the club to support bandmate Tom Parker, who was making a public appearance and celebrating his girlfriend Kelsey Hardwick's birthday.
A spokesman for the club said: "We cannot tolerate this behaviour from anyone, celebrity or not".
All this drama, and the boys' upcoming tour - which they recently announced will be their last for the foreseeable future so they can focus on solo projects - hasn't even kicked off yet.