Pallister believes the new manager is still searching for his best central defensive pairing with experienced duo Rio Ferdinand and Nemanja Vidic being pushed by Chris Smalling, Phil Jones and Jonny Evans.
He said: "You will have an idea which is your best partnership, but you can't expect them week in, week out 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 the sports science that they work with these days, they are at the very peak of physical condition.
"Everybody needs a rest at times. The games come too thick and fast and at too much of a high intensity, especially when you play at United.
"Everybody wants to beat Manchester United, so these games get extra-tough when you play some of the lesser teams in the Premier League.
"I think David Moyes is working out who his best partnership is, but there are still parts to play for everybody."
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