According to the report, the former United boss had dinner with the player after Real Madrid’s Champions League defeat to Schalke in midweek – and Kastrinakis says he could be tempted to leave at the end of the season.
But that would mean there would be no chance of Bale, who is also on Manchester United’s radar, leaving as well.
“If things go on like this at Real Madrid there will be a massive overhaul at the end of the season.”
Speaking on the Sunday Supplement, Kastrinakis said: “If things go on like this at Real Madrid there will be a massive overhaul at the end of the season and Ronaldo could decide he doesn’t want to be part of it.
“It all depends on Ronaldo. Do you think if he turned around and said ‘I want to come back to United’ then United would not have him yesterday? It all depends on what he decides to do.
“One of them will leave at worst. If Ronaldo leaves then Bale will stay put. If Bale leaves then Ronaldo will stay put, you can rest assured of that.
“My money would be on Bale staying because he is a personal bet of Florentino Perez, the president, who champions him and defends him after spending an exorbitant amount of money for a player of Bale’s calibre.”
Ferguson was pictured sitting alongside Jorge Mendes – the agent who represents Ronaldo and current United forward Radamel Falcao – in midweek.
And Kastrinakis says there are lots of barriers to overcome before Ronaldo could return to the club he played for between 2003 and 2009.
“He signed his new deal in September 2013 and that killed off the hopes of the fans that he would come back to Old Trafford,” he added.
“The thing is he is 30. He was 30 last month and has won back-to-back Ballon d’Ors since Rio Ferdinand confirmed stories that United wanted Ronaldo back and players were trying to convince him to come back. This was a story that ran for about eight months until Ronaldo signed his new deal.
“Can he come back? Should he come back? Obviously United are targeting Bale as well, who is five years younger.
“Between the two, in my opinion there is no comparison. Ronaldo is one of the top five footballers of all time. I don’t always like his behaviour, but the numbers are stratospheric. He knows United inside and out.
“Has Bale justified his 100million euro price tag? Absolutely not, even though he has scored big goals in big matches. Ronaldo has scored big goals in big matches and has done it in every other match as well for six years for Real Madrid.
“I think he can come back, but a lot of things have to fall into place.”