The 37-year-old has recently been struggling with a hamstring injury and has hinted that he could decide to retire at the end of the season.
Ferguson told The People: “Ryan is unbelievable – he’s 37 years of age but his fitness has not changed.
“I think there is another year in him. It is difficult to say at that age because they can hit the buffers just like that.
“Ryan will want to carry on because he knows he is fit enough.
“It is different with Gary (Neville). We will have to assess him. He has an injury again and it is difficult when you get injuries all the time in your 30s.”
