Chelsea sent a formal letter to Enzo Maresca to remind him of his responsibilities before his departure as manager as his relationship with the club began to deteriorate. The club were also so concerned about Maresca's treatment of players returning from injury that they put the club's head of physical performance on the bench to advise the Italian about when substitutions needed to be made.Maresca was sacked by Chelsea on New Year's Day after less than two years in charge at Stamford Bridge. The Italian won the Conference League and the Club World Cup during his time at the club but things unravelled quickly after he said he'd endured the "worst 48 hours" following victory over Everton. Maresca claimed he felt a lack of support around him and it subsequently emerged he had held talks with Manchester City. The 45-year-old had also told Chelsea he was talking to the Cityzens on three separate occasions with a view to potentially replacing Pep Guardiola at the Etihad. Chelsea subsequently announced his departure and brought in Liam Rosenior, from sister club Strasbourg, as the club's new coach on a contract until 2032.More details of the breakdown in the relationship between Maresca and Chelsea have now emerged, per the Mail. One key issue was Maresca's treatment of players returning from injury which caused a "major rift" between manager and club. Those upstairs at Stamford Bridge became so concerned by Maresca's refusal to substitute some players they sent him a formal letter to detail their concerns. Bryce Cavanagh, the club's head of physical performance, was also installed on the bench and instructed to remind Maresca when players needed to come off. Cavanagh also advised Maresca on times when players could stay on depending on how they had performed during the match in question. Chelsea made the move to put Cavanagh on the bench a week after Maresca's outburst regarding a lack of support and after seeing two players recently back from injury suffer further problems on their return to competitive action. Rosenior was generous in his praise of Maresca after replacing him at the helm but was also in no doubt about the size of the ask ahead in west London. He told reporters after arriving: "The biggest challenge in any club is creating the right culture, the right spirit, the right values. The talent level I've seen in training, the ability is world-class. I've got a fantastic group to work with and I'm very excited. Enzo did a fantastic job with these players. Tactically, he did a great job and they're at a great level."The turnover of managers now, regardless of the club, is huge. I'm aware of that. The pressure is there from day one. I am looking forward to it - I can't wait until tomorrow night. The players and staff have been nothing but supportive. It comes with the territory. If you're scared then there's no point becoming a coach. I am going to work 24 hours a day. I'm intense when I'm with the players."At a club of this stature, the fans want success and they have every right to want success. The fans should have those demands and standards. To win over the fans, I need to win games of football, build a team that represents them. I remember playing at Stamford Bridge where Jose Mourinho's team were at their best, there was a physicality in the team and that's what the fans demand. We are trying to build things in a different way. My job is to try and create a team where teams fear coming to Stamford Bridge."Add GOAL.com as a preferred source on Google to see more of our reportingRosenior enjoyed a strong start to life as Chelsea boss, overseeing a 5-1 win over Charlton in the third round of the FA Cup. However, he now faces a far tougher test as the Blues come up against Arsenal in the semi-finals of the Carabao Cup on Wednesday. Maresca failed to beat Arsenal in three attempts during his spell at Chelsea, while Rosenior has the chance to go one better than his predecessor on his first attempt. The winners of the tie will play Newcastle or Manchester City tin the final of the competition.