The Brazilian playmaker barely featured for the Serie A side and was sold to the Anfield club in January 2013 for a fee of £8.5 million.
Since then, the 24-year-old has established himself as one of the finest players in the Premier League.
“It was a great regret for me to have to sell him -- perhaps one of my greatest regrets in over 20 years at Inter,” he told ESPN .
“I have splendid memories of Coutinho, both as a footballer and of the lad himself. When he got here, it struck us how outstanding he was immediately - he was serious and wanted to work and you could see that he had all that was needed to go on and do what he has done so far.”
Despite this quality, the South American would find his chances at San Siro restricted and has flourished since moving to England. So far this season, he has scored six goals and assisted seven more in only 20 outings for the Reds.