A man suffered a cut to his face after an argument with a gang spilled over into violence, police said.
Paramedics were called to McDonalds, in Bank Hey Street, Blackpool town centre, after staff saw the attack over CCTV monitors.
But the man refused treatment and left without giving his details – leaving officers appealing for him, and any witnesses, to come forward.
The ‘serious assault’ happened at around 1.40am on Wednesday.
Information can be reported by calling 101, and quoting reference number LC-20170419-0077.