Nicol feels he still hasn't shown that he has enough to be Gerrard's heir, when the 32-year-old retires.
"Stevie G is only going to last for so long," he told talkSPORT.
"I still think they have to make a signing in the middle of the park. I don't think Jordan Henderson has shown or has had a run of games in the middle of the park to show he can [take over from Steven Gerrard].
"He can certainly do it physically. He can get around the field but whether he has the knowledge and the understanding of the game to play in there we have yet to see."