The Chilean played alongside Spain World Cup winner Puyol for three years between 2011-14 at Camp Nou, and the pair won the 2013 Liga title together.
He left to join Arsenal in 2014 before spending a dreadful 18 months at Manchester United where he was a shadow of the player he had been in north London.
"When I arrived in Barcelona it was said that it was the best Barcelona in history at that time,” Sanchez told UEFA's official website . “There was Guardiola, Messi, Xavi, Iniesta, who are not there now.
“There was Puyol, who for me is an incredible captain, the best I have had in my career so far.
“It was a nice thing, it teaches you to play football differently, with possession of the ball.
“In Barcelona, I learned a lot in the sense of improving myself. I played next to quality players who had won a World Cup, who every day improved in their physique and in their communication on the field.”
Both teams started their Champions League campaigns with draws on the opening match day and will be looking to take control of a testing group.
Inter dropped points in drawing with group outsiders Slavia Prague, whilst Barca were held to a stalemate by Lucien Favre’s Borussia Dortmund.
"At home they are very strong,” said Sanchez of his old club. “They have the confidence to play there. If we have one chance or two chances, we cannot waste them.
“I played with United there and we wasted three or four clear chances. Then they have one or two, they get in, and you're 3-0 down.
“If you want to beat Barcelona, you can't miss any clear chances.”