Speaking on Sky Sports, Merson said: "He is offside and, in football terms, it is criminal what Martinelli has done. I can’t express enough how you just cannot be offside when you’re looking along the line.
"He has got pace, he's electric so he's not someone who has got to try and nick a yard and play right on the edge. He can give someone a yard or two. I'll be surprised if he isn’t on the end of one in the dressing room when he gets in by the manager. He even knows. You could see it on his face after, he knew you can't do that.
"You cannot be offside when you look along that line. That is the one thing you cannot do. Do not be offside, it is as simple as that.”