Rangers are on the lookout for a new manager after they sacked Michael Beale on Sunday night following their defeat to Aberdeen at home on Saturday.
The Glasgow giants are likely to bring in the new boss during the next international break as they seek to get over their sluggish start to the season.
However, Ferguson indicated that the new manager will have the same issues that Beale had with the new summer signings.
He insisted that the new boys will need to do a lot more going forward if they are to convince anyone about their quality.
The Rangers legend also stressed that the new manager will have to find a way to make them work as for the moment he cannot get rid of them.
Ferguson said on the Go Radio Football Show: “Could they come good? I need to see more.
“Out of all the signings, only one of them has really shone through and that’s the goalkeeper Jack Butland.
“They need to show a hell of a lot more going forward.
“Will the new manager make that difference? Who knows? We need to wait and see.
“But he won’t have a magic wand to change it.
“He can’t go out and sell them or punt them or get rid of them or free them of their contracts.
“These guys are on long-term deals on big money that they wouldn’t get anywhere else.”
Preston boss Ryan Lowe has emerged as a target for Rangers and Kevin Muscat is also interested in the job.