Skipper Vidic and 32-year-old Ferdinand have formed the regular centre-back pairing in United's much vaunted defence for almost five years but the duo now face a challenge from a new batch of youngsters at Old Trafford.
United beat Tottenham Hotspur 3-0 on Monday night with Phil Jones, 19, Jonny Evans, 23, and Chris Smalling, 21, making up the back four, along with Patrice Evra, and the trio made a lasting impression on the United manager.
While Vidic is out for three weeks with a calf injury, Ferdinand could be fit for United's Premier League match with Arsenal at Old Trafford on Sunday, but Ferguson said it will be a tough decision as to how to restore him to the team.
"Rio and Nemanja are aware of the abilities of the young players. There is no question about that," Ferguson told The Sun. "When they are both fit, or one of them is, I will have a decision to make."
The United team that beat Tottenham at Old Trafford was the second-youngest Ferguson had fielded in Premier League history, with an average age of 23 years 191 days.
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