The Sun says Portugal winger Nani was already feeling uneasy after he was left out of United's Champions League final side by boss Alex Ferguson.
Now, with the £20million signing of England winger Young, he will be fearing more time on the bench - with the former Aston Villa player, 25, set to start the season.
There were rumours mid-season that the player was looking for a new challenge away from Old Trafford, something which he dismissed in the wake of the 3-1 Wembley defeat to Barcelona.
Nani, 24, said: "I'm very happy at United. This has been my best season but I can do much better.
"I'm still young and will get more opportunities."
United return to training on July 4 and Nani will seek crunch talks with Ferguson to see exactly how much first-team action he should expect in the new season.