Neither player has hit top form in recent weeks, but Ferguson insists the duo deserve their place.
"I think Jones and Smalling should go but they haven't played a lot of football for us this season at centre-back. Monday night was Smalling's first game at centre-back for a long time because of the form of Rio Ferdinand and Jonny Evans.
"Smalling and Jones have had one or two injuries as well. You go back to what you've got left and you have John Terry, Rio, Gary Cahill and then you've got Jones and Smalling - there isn't a lot after that," said Ferguson.