Young, 25, last week completed a £16 million move to United, where he is expected to compete with Nani for a place in Sir Alex Ferguson's team.
On the eve of Young's signing, it was reported that Nani was perturbed and considering his options, but the Portuguese has insisted he is not concerned by the new arrival.
"Of course I have to welcome everyone they sign," Nani said. "I think Man United is a fantastic club.
"When they bring in new players, they know if it is good for the team or not, and this [Young signing] has to help them. It is good for the team - we want more [players] to help us to win trophies."
Nani also said he had the fight in him to keep Young on the substitutes' bench, pointing to his experience jostling for playing time with former United star Cristiano Ronaldo.
"I've been there when Cristiano was there," Nani said. "Cristiano was one of the best players in the world."