Bale, 25, was the subject of criticism from fans and media as Real failed to win La Liga and the Champions League.
The Wales forward was linked with a return to the Premier League but has said he will stay at the Bernabeu.
"My own opinion is that we will probably see, for one reason or another, Cristiano move from Madrid before Gareth," Toshack said.
Forward Ronaldo, 30, has been a Real Madrid player since signing from Manchester United for £80m in 2009.
Bale joined Real from Tottenham for a world-record fee of £85.3m in 2013, helping the Spanish club claim their 10th European title in his first season.
The Welshman scored 22 goals in his debut campaign followed by 17 in his second.
"You do need time to adapt and obviously for the money they paid for Bale and at the age that he is, he's still got a lot to do," Toshack added.
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"I hope Gareth will get the opportunity to play in an area of the field where he can do most damage.
"I'm not so sure wide is Gareth's best position. I think Cristiano has got a bit do with that.
"He was always a number seven, but likes to play left side and I think Gareth suffers a bit for that."
Toshack, who was Wales manager when Bale made his debut as a 16-year-old in 2006, had two spells at Real Madrid. The Spanish side appointed Rafa Benitez as their new coach on 3 June.
Former Liverpool and Chelsea manager Benitez was in Cardiff recently to see Bale score in Wales' 1-0 win over Belgium in a Euro 2016 qualifier.
Ex-Liverpool and Cardiff City striker Toshack now coaches Moroccan side Wydad Casablanca and believes Benitez is a good choice as Carlo Ancelotti's successor.
"Rafa's got all the credentials, there's no question about that," Toshack added.
"Rafa was at Madrid at the time I was there, working with the junior sides.
"They're full on with Benitez now in Spain, in particular the newspaper Marca.
"Everyday it's 'Rafa's going to do this and Rafa's going to do that' but we just have to wait and see."
Ex-Real Madrid coach John Toshack believes Gareth Bale will outstay Cristiano Ronaldo at the Spanish club.