There were concerns that the Portugal international would not be able to shake off a thigh injury in time to feature in Wednesday's showdown with the Dutch side, goal.com reported.
He, however, took part in training with the rest of the squad on Tuesday and looked set to be given the green light to play.
There is less positive news over the fitness of captain Giorgio Chiellini, meanwhile.
The Italy international defender was already a doubt for the first leg in Amsterdam with a calf injury and, having missed training on Monday, he was forced to undergo a session away from the group.
Former Liverpool midfielder Emre Can is also expected to miss the game after he also had to train separately from the rest of the Juve squad as he continues to struggle with an ankle problem suffered against AC Milan.
That could see Sami Khedira, who only recently returned to action following a heart problem, take his place in the team in what would be his first start since February 15.
Should, as now expected, Ronaldo feature from the start against Ajax, it will be his first appearance for Juve in four matches.
Having been rested for the 2-0 defeat to Genoa, Ronaldo subsequently injured his hamstring on international duty with Portugal where he had to be withdrawn after 30 minutes of the 1-1 Euro 2020 qualifying draw with Serbia.
That meant he missed Juve's three matches after the international break, including the 2-1 triumph over AC Milan that has put them within touching distance of another Serie A crown.
A draw or win in Saturday's clash with 16th-placed SPAL will see Juve win an eighth consecutive Italian top-flight title and ensure Ronaldo will have won league titles in England, Spain and Italy.
With the Serie A title all but clinched, Massimiliano Allegri's side will be hoping it can make significant progress in Europe and, should it manage to advance past Ajax, it will then face either Manchester City or Tottenham in the semifinals.
And Juve will likely be looking to Ronaldo for inspiration, with the 34-year-old scoring an incredible hat-trick to ensure the Italian side recovered from a 2-0 first-leg deficit to beat Atletico Madrid and advance through to the quarters.