United are reeling after Sunday's 4-0 defeat at Everton.
"Star players, those five, they can be the best in their position, but all of them in this moment in time are well below their standard.
"I went to both Barcelona games. Marcus looks off it at the moment. Whether he's carrying an injury. something is not right, or the season has caught up with him.
"Romelu Lukaku – he doesn't turn up in a big game. That's been levelled at him for a number of years now.
"And Martial he's just come back from injury, but he looks like he's back in that sort of ambling mood again.
"De Gea looks nothing like, he looks distracted. You've got contract talks that are going on between five or six players, which is distracting at this time."