Goalkeeper Reina says he is disappointed over the way that Liverpool handled the deal and claimed they never told him of the season-long loan.
In an open letter on his website, the 30-year-old Spanish ace says he wasn’t informed he was moving to the Serie A side until after the deal was completed.
Reina had originally planned to join Barcelona when keeper Victor Valdes announced he would quit the Nou Camp at the end of last season.
But Valdes then changed his mind after Liverpool had already decided to sign Simon Mignolet from Sunderland for £9m and were planning to bring in a similar fee for Reina.
Instead, they were left with the possibility of having two top keepers and let Reina join former Reds manager Rafa Benitez at Napoli.
But Reina says he told Liverpool that he would be interested in extending his contract at Anfield if an offer from Barcelona wasn’t forthcoming.
He said: “A lot has been made about me informing the club that if an offer came in from Barcelona that I would have liked them to consider it. But I had also spoken to the club about the possibility of extending my contract if the offer was not made.
“I told the manager that I wanted to play for Liverpool and that Barcelona would only become an option for me if the opportunity arrived.
“When it didn’t come, I was happy to fight for my place. I was surprised that Liverpool decided it was in the club’s interests to send me to Napoli.”
The Spaniard also thanked Kop fans and believes the club can challenge for major honours this season.
He said: “The supporters deserve the best of times and it would give me so much pleasure to see Liverpool back where they belong, challenging for trophies and getting back into the top four. I honestly believe that Liverpool can reach those levels.”