Talking about his departure recently on Sky Sports' Goals on Sunday, the Italian announced losing John Eustace to Derby County proved to be a major factor in the staggering fall of Zola's time at Watford.
'It has been very painful because I enjoyed my time there and I enjoyed the company of people I worked with,' said Zola.
'But obviously something had to be done because it wasn't clicking.
'I think there were things that didn't work out the way we wanted. We lost players from last year that were very important players.
'The players that came in to take their place were unfortunately not able to fill the gap. So they were a big miss.
'We had players that didn't play much but were so important within the team, for example John Eustace.
'In the case of John, we could have kept him. There were some questions about his physical condition and he hadn't played much for me because of that reason.
'So there were a few things that didn't go the way we wanted.'
The fall of Zola's tenure at Vicarage Road came to an abrupt end after a nine-match winless streak saw them plummet from the play-offs to a mid-table position, which is where they remain to this day.
Incidentally, Watford's plummet seemed to coincide with the Rams' rise up the table, which heavily involved former Hornet John Eustace.
The 34-year-old has played 31 times for Derby this season, becoming an important and integral member of their first choice eleven. Which usually see's him sat behind the exciting talents of Will Hughes and Craig Bryson.
Watford will still look back on last season and wonder what might have been for them, if not for an unpredictable and tight play-off final. However, for now they will focus on the future and what it now take for them to get promoted.