They were once a part of the world's deadliest attacking trio, along with Luis Suarez.
Neymar has starred for PSG, scoring 20 goals in all competitions - 11 of those strikes in Ligue 1 - but in an interview with ex-Brazil global Zico via YouTube, former Barca striker Ronaldo said: "Sportingly, the decision is a step back".
Neymar scored from the penalty spot in Wednesday's 2-0 French Cup quarter-final victory over Amiens, taking his tally for the season to 21 goals in all competitions.
However, former Barcelona star Ronaldo believes the move was a step down in terms of his footballing development.
In an interview with Zico, the Brazilian said: 'Sportingly, the decision is a step back.
"But there are challenges that everyone seeks".
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Neymar has been impressive since joining the Parisians from Barca.
I personally agree with what Ronaldo had to say about the player.
He threatened to ruin his legacy among Barcelona fans though when he jumped ship for Ligue 1 giants PSG five months ago.
PSG's justification for leaving Neymar out is treatment for costal cartilage pain - the Brazilian and captain Thiago Silva did not train with the rest of their teammates on Friday but both were with the squad on Saturday.
Having already played for bitter rivals Barcelona, a move to the Bernabeu could not be the best idea for Neymar - if history is anything to go by.