Sir Alex Ferguson continued his summer shopping on Thursday when wrapping up the deal to bring Young to Old Trafford from Aston Villa.
The arrival of the England international has prompted suggestions that Valencia, who performed well towards the end of last season after battling back from serious injury, could be vulnerable.
But while Valencia is aware of the challenge he faces, he insists it is one that he will take on with relish.
"I heard about this on the news," Valencia said. "I do not fear his arrival. "The season is long and under Alex Ferguson everyone will get their chance in United's key matches.
"Ashley is a good footballer and I believe he will help us towards more success. As for myself, I have two more seasons left at United and I am convinced I will fulfil those. And maybe a few more years too."
Commenting on reports linking him with Real Madrid and Juventus, he said: "There are rumours about other clubs but I have no news on that."