Renault Laguna 1.8 no compression?

Hey guys need advice have a 02 1.8 laguna only building about 7 bar compression a cylinder 1 and about 13 bar in the rest.Put some oil in and brought it up to about 8 bar if even that.Am suspecting a burned exhaust valve maybe but am not pushed on taking the head off as the customer refuses to believe such a new car(5 years old ha)can have such a problem and isnt to big on spending some cash so any advice welcome thanks...