Mario Giuffredi, who represents Hysaj, has supported his client after recent criticism of his form, and said the right-back could have left for Stamford Bridge and the Premier League.
Speaking to Radio Kiss Kiss Napoli (h/t Goal), Giuffredi said:
"Those who criticise him probably never make mistakes, but the rest of us are mere mortals.
Without that clause he probably would have gone to Chelsea this summer.
People forget that he was one of the best two or three full-backs in Europe last season. Then it just takes two or three matches for him to become a donkey.
“I always say to let everyone talk and then respond on the pitch."
Sarri was shown the door by Napoli as rumours of a switch to Chelsea grew, and the coach immediately raided his former team for the signing of Jorginho. It now seems De Laurentiis made sure Hysaj didn't follow.
The breakdown of the relationship between Sarri and De Laurentiis appears to have damaged any chance of the Blues manager returning to Naples to handpick from his former players.
De Laurentiis recently explained he lost faith in Sarri in the final months of his tenure.
Speaking to Corriere dello Sport (h/t Alex Richards of the Mirror), the Napoli supremo said:
"Sarri? I thought I had met a coach who would stay at Napoli for a long time. At a certain point it became a question linked exclusively to money.
Suddenly, it was established by the media that his contract must be adjusted. So what is the value of an agreement just signed? We had already gone from €700,000 to €1.5 million.
I also once heard him say that for his next contract, he wanted to get rich.
Sarri's declarations of love for the city? I believed it, but then I wondered: 'What if he was using me as a bank?'"
Hysaj followed Sarri from Empoli to Napoli in 2015, and has clearly been one of the Italian's most trusted players over an extended period.
The 24-year-old's technical ability has seen him become revered in Italy, and he would have been perfectly at home if he had moved to the Bridge.
The Albania international played 43 games for his club in Serie A and Europe last term, and his versatility on both flanks makes him a vital squad member.
Chelsea have a settled pair of first-choice full-backs, with Marcos Alonso and Cesar Azpilicueta both stellar performers for the west London giants.
The pair's consistency negates the need for a concerted move for Hysaj, with the Blues having to strengthen in other positions.
As the long-term future of Eden Hazard remains unsure, Chelsea will be eyeing attacking midfielders across the world rather than defensive talent.