https://metro.co.uk/2018/05/30/why-chelsea-are-in-a-state-of-limbo-over-maurizio-sarri-and-antonio-conte-7590524/
'Sarri takes home a relatively modest £1.3m a year, but his release clause is set at £7m. That expires at the end of May, at which point Sarri will be able to resign at a cost of £500,000 but Napoli will be due a compensation package from any club he joins afterwards. If, as it seems, Chelsea are unwilling to meet Sarri’s release clause, then they will hope to negotiate a lower fee once the May 31 deadline has passed. Reports in Italy suggest a fee of £3.5m would be accepted.'