The Premier League gets underway on Saturday with United defending the trophy - their 20th league title - which they won in May.
New manager David Moyes - who succeeded Sir Alex Ferguson in the summer - will take charge of the Champions for their first league game at Swansea - live on Sky Sports' Saturday Night Football.
And whilst Moyes has so far failed in his attempts to sign midfielder Cesc Fabregas from Barcelona, Vidic is happy with United's strength in depth.
"We have a good team, we have a big squad - we are the champions," he told Sky Sports News.
"We have a lot of young players in the team and over the last two years they have improved a lot, which is important for the team and the club.
"I believe we are strong enough to compete for all trophies - one or two more signings would be good for the team but things are good.
"Cesc (Fabregas) is a good player but it's not up to me to say who we need or not - any player who comes here will be accepted, just as I was when I came here.
"But it's not something we think of much - we just try to focus on our game and to help the manager achieve what we really want. That's our aim."
You can watch Manchester United begin their title defence at Swansea live on Sky Sports 1HD on Saturday at 5pm