Ferguson feels for Wenger after Arsenal's Euro elimination this week and said: "Arsenal have had so many injury problems. If you don't have your best players it is difficult to get the best result.
"But it is not just having your best players but having the best squad available, to enable you to change when you need that bit of freshness."
Fergie and Wenger have been at each other's throats for the last decade.
But the Red Devils chief defended the Frenchman's recent record and spending policy in the January transfer window.
Ferguson said: "It just underlines how hard it is to win the Premier League. It is not easy. It is a tough league.
"It is not easy to buy players in January - there's not a lot you can do then."