Nani is currently sidelined with a hamstring injury, and reports have increasingly linked the Portugese with a move away from Old Trafford.
But Ferguson has quashed rumours of the 26-year-old exiting the club, insisting that his fitness is the only thing preventing him from playing.
"He’s injured," Ferguson told the club's website. "His contract’s not up for a year and a half.
"We need a Nani. He offers something different from the other players. He’s an incredible talent, the boy's a great talent. Unfortunately, he’s injured at the moment so we sent him over to Dubai for a break and hoping a bit of warmth will help him in his recovery.
"He’s not far away but he’s far enough away. I don’t think I’ll get him back until probably the middle of January. It’s a hamstring injury he’s got.
“A player like Nani has never had a hamstring injury ever – I don’t think he’s ever had many injuries with us. But he’s got it right in the top and it’s a bad one."
When asked if Nani has a future at Old Trafford, he replied: "Yes. Absolutely. Why would I want to let him go?
"Obviously his people have been negotiating with [chief executive] David [Gill] about a new contract but I don’t know what stage we are at with that. But we won’t be letting him go."
Meanwhile, Ferguson was also quick to refute reports that a deal has already been agreed to bring Dortmund’s Lewandowski to the club at the end of the season.
"It's nonsense," he asserted. "Absolute nonsense."