Neymar spent four years at Barca, scoring 105 goals in 186 appearances and helping the club win two La Liga titles, three Copa del Rey trophies and the Champions League.
He then became the most expensive player in history when he completed a £198million move to French club PSG in 2017.
Neymar has enjoyed more individual success in Paris and won a host of domestic trophies, but has been unable to enjoy more European success, with PSG yet to win the Champions League.
Souness still ‘doesn’t understand’ why Neymar decided to leave Barcelona and claims he chose an ‘easier life’ by joining PSG.
He wrote in a column for The Times: ‘One of [new PSG manager] Mauricio Pochettino’s main challenges will be getting the best out of his stars such as Kylian Mbappe and Neymar.
‘They both have stellar reputations but they need to live up to them. I’m less worried about Mbappe as he has only just turned 22 – time is very much on his side to become a great player.
‘But I don’t understand why Neymar left Barcelona in 2017 when he was playing with Lionel Messi.
‘I don’t see that as someone saying they really want to challenge themselves.
‘It was definitely a step down to leave Barcelona at that time. What for? More stardom and an easier life, I guess.
‘I’m not sure what that says about him.’
He said: ‘I return to the club today with a lot of ambition and humility, and am eager to work with some of the world’s most talented players.
‘This team has fantastic potential and my staff and I will do everything we can to get the best for Paris St-Germain in all competitions.
‘We will also do our utmost to give our team the combative and attacking playing identity that Parisian fans have always loved.’