Merson told Sky Sports: "It was a bit of a worrying performance from Salah at Wembley. I don't think I've seen a player play that badly before in a football match.
"But that can be Salah. He can go missing for a few weeks before going on a run of scoring in ten matches on the trot or smashing in a hat-trick. One thing that might be difficult for him this season is playing in front of Jeremie Frimpong. Compared to Trent Alexander-Arnold, he's more like an attacking winger.
"There's a major problem down that side of the pitch, even more so than last season."