Manchester United boss David Moyes is baffled by the contrast of their Champions League and domestic form.
United's 1-0 win over Shakhtar Donetsk at Old Trafford ensured they sealed top spot in Group A and will avoid most of their fellow heavyweights in Monday's last-16 draw.
"If I had the answer I would have solved it by now and it would all be okay," he said.
"I do believe there is a different style and you can tell the players here are used to it.
"They are well experienced in European football so I think they are more than capable of playing at this level. They are comfortable with it.
"They are also very comfortable in the Premier League but at the moment they are not showing it."
