Eduardo Vargas was unveiled as a Gremio player on Sunday and used the event as an opportunity to attack former club Napoli, where he says he was "not happy".
Vargas, 23, only signed for the Serie A side in December 2011, costing them a staggering £11.5 million after scoring 29 goals for Universidad de Chile during the previous season.
The Chile international failed to settle into life on the peninsula and has joined the Brazilian club on loan for six months in hope of recapturing his previous form.
"I had a good career in Chile, now I want to repeat that in Brazil and become one of the best players in the Copa Libertadores," he said.
"I was not happy in Italy. I didn't feel good on my debut and played badly, then I lost my confidence and was never able to play consistently.
"It was my Napoli team-mate Bruno Uvini who recommended Gremio to me. He told me all about this city, how relaxed it was and how playing for Gremio would be good for me."
Vargas played 28 times for the Partenopei and netted just three goals, all of which came in a single Europa League match against Swedish side AIK. The short-term move has seen Napoli recoup just £1.6 million of their initial outlay.