Fergie claims that the duo’s time has come to make the big breakthrough at Old Trafford.
United have already secured qualification from Group B.
Ferguson said: “I will be making changes (against Besiktas). Not a lot, but enough just to freshen it up.
“It’s a problem keeping players happy, but everyone has that when you have a squad of players.
“We use the League Cup for that and, if we can qualify early enough in the (Champions League) group, we can then use the likes of Welbeck.
“He will definitely play (against Besiktas) and Macheda too probably. They are the ones that need to be challenged.
“They’ve reached a point, and it happens in football, when a footballer has the ability to be a top player and you recognise that.
“You have to give them the challenge. If you don’t, they lose the scent.
“But this club has been good at recognising that over the years.
“It’s unfortunate for players above them, but when the likes of Nicky Butt and Paul Scholes came through, we thought they were certainties, but we had to give them a chance. And we did.
“That’s the nature of football. A young player turns the corner and takes someone’s job.”