A tower of strength in the centre of Manchester United’s defence since he arrived at Old Trafford from Russian football six years ago, Nemanja Vidic has been badly missed by Sir Alex Ferguson’s side this season.A bad night in Basel last December, during which the Red Devils were dumped out of the UEFA Champions League at the group stage, was worsened by a knee ligament injury which ruled the Serb defender out for the remainder of the season. Ferguson has had to rely on youngsters Jonny Evans, Phil Jones and Chris Smalling in the meantime and will be without the 30-year old for United’s crucial Premier League run-in.Having been knocked out of the FA Cup in the fourth round by rivals Liverpool and eliminated from the UEFA Europa League easily by Athletic Bilbao, the championship now represents United’s only chance of silverware for 2011/12. But four-time Premier League winner Vidic has warned that it is a ‘long season’ and could be decided by United’s trip to Manchester City on 30 April.In an exclusive interview with FIFA.com, the centre-back discusses the genius of Ferguson, why Barcelona are the best team in club football, his decision to retire from international action and his plans to become a coach in the future.FIFA.com: You were outstanding during the first half of the year and chosen as a member of the FIFA/FIFPro World XI. What does that recognition from your colleagues mean to you? Nemanja Vidic: I think it is the best reward you can have. When you are rewarded by the players it means a lot. It’s hard to explain the feelings. It feels like a dream has come true.Can you explain Sir Alex Ferguson’s 25 years of success with Manchester United? What makes him so special?It’s obviously the experience he has, and knowledge, and the titles he has won over the years speaks for itself. I think first of all the knowledge to understand the players and to know how to deal with them is what is best about him. To win so many trophies like he does, and to be with this club 25 years, I don’t think there is anyone else like him.United are still battling in the Premier League title race. Do you think the second game against Manchester City will be the decider?It’s still a long season. It could be that game is decisive for the title, which is something really good for the fans and good for the league, and if you win that game you definitely deserve to win the title as well.What is the latest news on your injured knee?It’s doing well. It’s slowly getting better. Obviously it will be hard to be back for this season, but for next season I hope I will be fit and hopefully I will be the same as I was before the injury.An important player this season is Phil Jones, especially now that you are unfortunately missing through injury. How do you rate his development this season?I think he has big potential. He is young and still has to learn. But obviously, how he has played the first half of the season has surprised everyone and I think if he keeps going he has a big future and is a big player, not just for United but for the world of football.Who is the best player you have played with and the best player you’ve played against?The best player I have played with is [Cristiano] Ronaldo, definitely. I would say Barcelona as a team is the hardest team we face and I’ve faced personally. And I would say [Lionel] Messi, the way he plays is difficult to cope with and I would say the whole team, Xavi and [Andres] Iniesta, have left a big impression on me.Barcelona are probably the best team in the world at the moment. What makes them so strong?I think that the biggest thing that makes it difficult to play against them is because they play without a striker. When you play without a striker they are moving the ball all over the pitch, they have the possession, and that makes teams frustrated. And, obviously, they are technically very good and their knowledge of the game is really good and they know what they are doing. They’ve been doing it for years and years. Even when you know what is going to happen, they make it happen. You have to say they are a great team.You have come up against Messi on several occasions. What is it like to play against him as a defender?He is a great player. I think it is not just him, it is a generation of players they have in Barcelona - Xavi, Iniesta. I think they are definitely one of the greatest teams ever. I think the goals he has scored and the trophies he has won make him what he is.You stepped back from the Serbian national team. Is that a final decision or is there a chance you might return?I gave my decision, and obviously after long thinking. It was a very difficult decision and it’s hard to announce but once made, it’s done and it’s not something I’m looking now to change. I’ll always be there for the national team if they need any help in terms of anything.