The 25-year-old England back was with fellow Saracens players, their wives and girlfriends, before someone unknown to them approached the group and started arguing with the 25-year-old.
"A brief altercation occurred, which resulted in a friend of this stranger attacking Chris Ashton with a glass. The Saracens winger suffered two minor cuts on the left side of his face, but neither required stitches," a statement read.
Edward Griffiths, CEO of Saracens, added: "Since arriving at the club, Chris has proved himself an outstanding member of the Saracens family, on and off the field. It is a reality that well known sports people are provoked by strangers and subsequent events are instantly tweeted.
"People will inevitably see this story and say an England rugby player is in trouble again. For clarity, Chris Ashton is not in trouble at all. On the contrary, he was celebrating an anniversary with his girlfriend and showed admirable restraint."