"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.
"But you want to try and win the group. A lot has been said about me being inexperienced in the Champions League so I am happy to top the group."
Moyes confirmed Nemanja Vidic, Patrice Evra, Marouane Fellaini and Chris Smalling had all missed out through injury, although added none of the problems were serious.
Now United must get their domestic form back on track at Aston Villa on Sunday.
And in that, they have the good wishes of Shakhtar coach Mircea Lucescu, who cast aside the disappointment of his side sliding into the Europa League to give Moyes his backing.
"I would like to congratulate Manchester United on their victory and wish them good luck for future games," said the Romanian.
"I hope this result will help them to revive their play in the Premier League."