Gary Pallister believes the days of two centre-backs being regarded as automatic selections at Manchester United are over.
The ex-Reds defender forged a successful partnership with Steve Bruce at Old Trafford after joining from Middlesbrough for a British record fee of £2.3million in 1989.
After Nemanja Vidic and Rio Ferdinand became United's top pairing towards the latter years of Sir Alex's reign, the options open to David Moyes in the heart of the back four are impressive with Jonny Evans, Phil Jones and Chris Smalling all pushing the experienced duo for a regular starting spot.
"There's not so much of that anymore," Pallister replied, when asked by ManUtd.com about the importance of a regular partnership. "You can't rely on two players to play week in and week out.
"We've seen that and Sir Alex himself did that. You have an idea which is the best partnership but you can't expect them to play every game. The demands are far too great now. Footballers today are more athletic than they were even in my time. These guys have six-packs and sports science behind them. It means they are in the very peak of physical condition but everybody needs a rest at times.
"The games come thick and fast with too much of a high intensity, especially when you play for Manchester United as everybody wants to beat you. So even against the lesser teams in the Premier League, it's