The manager stated that despite the fact the duo had spent time recovering in Qatar during the club's warm weather training camp, they will not be back in time to face the London club.
"Jonny Evans and Ashley Young are still not 100 per cent fit," Sir Alex told reporters.
"We had a good week training in Qatar and it was a great time to go there – we couldn't have picked a better moment actually when you consider the weather we’ve had here.
"So it’s worked out very well for us and hopefully we get the benefit from that. It was always the plan at some stage to do that this January. It couldn't have worked out better for us.
"Ashley Young is not far away. He trained a bit in Qatar. Not a lot, but at least he is on the road back and he has always been an important player for us.
"Jonny is just taking a bit longer than we thought. But he did a bit of training in Qatar. Again, not a lot, but he is on the way back. The bonus for us, of course, is that Phil Jones and Chris Smalling are both back. So we're not so bad in that department."
Ferguson did, however, confirm that both players would return in time for the club's Champions League tie with Real Madrid, as United continue to challenge on three fronts.
He added: "Both of them will be fit for that. I would hope to have a fully fit squad by the time those games come around."
The United boss was also adamant that the FA Cup remains an important competition and was confident his side is happy to face anyone on their way to the final.
"We haven't done as well in the FA Cup for a few years now," he continued. "It's a cup which has fantastic appeal given our record in it. We have benefit of the home draw. We'll take that any time. It's going to be a challenge for us but we would play anyone at the moment.”