The veteran winger came under fire for a series of below-par performances this term, although he did appear to return to form on Boxing Day suggesting that this season may not be his last.
"How can people criticise a player like that?" said Ferguson.
"He has given us 20 years and has done so well.
"It is a problem for him because he wants to play more but at his age I cannot afford to risk that.
"He was amazing on Wednesday and it is simply beyond belief that anyone can criticise that. I do not understand it."