Manchester United boss Sir Alex Ferguson has put Rio Ferdinand and Nemanja Vidic on notice after their shaky 3-2 win at Southampton.

The once-formidable partnership looked shaky in their first game together since a 2-1 Champions League defeat to Basle last December and Ferguson knows they need to improve.

"I think it is an important issue, there's no question [about it]," he said.

"I think throughout the years we've had two centre-backs playing regularly that impacts on the whole team, right from Steve Bruce and Gary Pallister, to Jaap Stam and Ronny Johnsen.

"Last season when we had Jonny Evans and Rio Ferdinand for a long period our performance was at its best."