The Aussie stopper has been invited to train with Rangers for the next 10 days. Current keeper Neil Alexander, who dropped a clanger in the 1-1 draw with Elgin, is in negotiations with the club about a new deal but is unhappy at the length of the contract that is on the table.
Ryan is already in the Australian squad and has been first-choice keeper for A-League side Central Coast Mariners for the last two years.
Nine-in-a-row hero Fergie turned out for Ryan's side and is currently in charge at Perth Glory, and reckons a move abroad is the next step in the youngster's career. He said: "He has a tremendous amount of first-team experience already. He is quite exceptional but, right now, you would have to see that he has an enormous amount of potential.
"To me, having the right people behind him and working him hard, he could really go on to be a fabulous keeper.
"He has already broken into the national side, he has been spoken about in glowing terms for years and there have been a few top English clubs sniffing around him.
"He is most definitely a guy you would say would be worth a punt on.
"He only has a few months left on his deal and, if Rangers were to get him and keep him for a couple of years, I would go so far as to say they would make a significant profit on him if he then wanted to move on again in his mid-20s.
"He does need a bit of work and he is a bit raw, but he definitely has a lot of talent."
Ferguson played alongside Rangers legend Andy Goram during the club's domination of Scottish football in the 1990s, and he believes Ryan can hit those heights.
"He is nowhere near that just now, but he is only 20," he said. "The sky is the limit for him.
"He has all the qualities required to make it at the very top level in football. I think he will relish the week or so he has now at Murray Park.
"He'll enjoy the facilities and the coaching and I think Ally will really like what he sees too.
"He is definitely one of the best young goalkeepers I have seen."
And Ferguson insisted that being able to cope with the demands of playing at Rangers wouldn't faze Ryan, should the trial become something more substantial.
"He has played in grand finals here and in some other very big games and has handled himself very well," he said. "He is almost certainly the future first-choice goalkeeper for Australia.
"I don't think he would cost too much money right now, but he is the kind of player I would expect to be worth a lot two or three years down the line."
Meanwhile, Kenny Miller has also been linked with a return to Ibrox. The 33-year-old is under contract to Vancouver Whitecaps in the MLS, but he has been training at Murray Park over the last few weeks.
Gers can't register any new players until September 1 due to their transfer ban but they can sign players on pre-contract agreements.
Miller said: "There is no doubt I would come back. I'd definitely do it, it's whether it could happen. You never know in football.
"Rangers hold a strong place in my heart. When I was a kid I always wanted to play for the club.
"I used to come through with my cousin to watch games regularly and I always said it was my dream to play for Rangers. I managed it not once but twice.
"It didn't quite work out the first time, but I was lucky enough to come back and had a great two-and-a-half years where we won leagues and cups.
"It was the best time in my career in terms of form and goalscoring. I had a lot of highlights."