United are at the bottom of Group A heading into their penultimate group stage match and know a win is needed if they are to have any realistic chance of reaching the knockout rounds of the competition.
Galatasaray secured a famous 3-2 win when the sides met at Old Trafford last month and Ten Hag knows his team will need a huge improvement if they are to have any chance of winning in such a hostile environment this week.
Mainoo shone in his first Premier League start against Everton at the weekend, though there have been some doubts about whether or not he can play again so quickly in such a big match.
Those concerns were put to Ten Hag at his pre-match press conference, but he insisted he has no worries about potentially playing the teenager again. “No. We dont have fear,” he said. “If players are good enough, they are old enough.”
It has been Mainoo-mania since his impressive performance at Goodison Park and Ten Hag was also asked how difficult it will be for the youngster to stay grounded amid the hype.
The United manager insists he doesn&apost currently have any worries about Mainoo becoming distracted and says he won&apost be afraid to tell him if he ever believes it becomes an issue.
He added: “We are very pleased with the performance, but it is one performance. You have to do it on a consistent basis. Kobbie is so mature, he knows that. We are confident he will do it, but first you have to prove it, as we all have to prove. You are only as good as your last game.