Manchester United midfielder Shinji Kagawa will miss the next three-four weeks with a knee injury suffered against Sporting Braga in the Champions League on Tuesday.
The Japan international was replaced at half-time after limping for much of the first half.
Kagawa will miss the double header in the Premier League and League Cup against Chelsea, and the games against Arsenal, Aston Villa and Norwich City domestically, and Braga and Galatasaray in the Champions League.
"It's a knee injury similar to the one Ashley Young had," revealed Ferguson. "I think playing on with the injury did not help the situation. It's disappointing for him."
However after the news that Ashley Young had returned to training last week, United have been boosted by the news that Smalling could be in contention for a return in the coming weeks.
In addition, international counterpart Phil Jones, who was the mainstay on a much changed United defence last season, is also set for a return to training following five months out with a knee injury.
Neither player has featured for club or country this season, injuries which forced them out of the European Championship and the Olympic Games, but Ferguson admits the England defensive duo could return in the near future.
"Smalling is back training on the football side of things," added Ferguson. "Phil Jones will hopefully start football training a week on Monday.
"It's a big bonus to have Smalling back and everyone else is fit."
Kagawa had enjoyed an encouraging start to his United career, fitting in seamlessly in a midfield including Michael Carrick and Paul Scholes, allowing the former Cerezo Osaka player plenty of freedom in his early days at Old Trafford.
The 23 year old has already netted twice this season in the win over Fulham and defeat to Tottenham Hotspur, and his influence as the season comes to the boil around the festive period will be crucial.