Some fans were left puzzled as to Why Dunn was being taken off against Chelsea, even though he had hardly put a foot wrong.
But Big Sam had noticed that the player was starting to struggle and made the switch as a precautionary measure, especially with such a big game coming up this weekend.
Allardyce told the club’s official site: 'I wasn't liking Dunny stretching his calves and things like that.
'It was telling me that if he carried on he might tweak a muscle again, so we took him off and put Morten in there and then of course we felt Niko had battled a lonely battle so we put a fresh pair of legs in with Jason Roberts.
'So in the end it worked very well.'