Rafael Benitez has said he will leave Chelsea in May and described the decision to give him the title "interim manager" as a "massive mistake". After beating Middlesbrough 2-0 in the FA Cup fifth round, the Spaniard also criticised some of the club's fans. He said: "Chelsea gave me the title of interim manager, which is a massive mistake. I'm the manager. "The fans are not helping us. At the end of the season I will leave. They don't have to worry about me." Benitez's defiant post-match interview came after the former Liverpool manager was once again targeted by a section of his club's own supporters. The 52-year-old has always been unpopular with some Blues fans since he took over from Champions League-winning manager Roberto Di Matteo in November. A section of the club's supporters were unable to forgive or forget Benitez for his association with Liverpool, and the acrimonious rivalry formed with then Blues boss Jose Mourinho. Benitez outwitted 'The Special One' in the 2005 and 2007 Champions League semi-finals and the 2006 FA Cup semi-finals, and directed some barbs towards the club. "I have been in charge in football for 26 years, I won the Champions League, I won the Fifa Club World Cup, the FA Cup, the Italian Super Cup, the Spanish league twice, nine trophies - all the trophies you can win at club level," said Benitez after a comfortable victory at the Riverside. "So this group of fans are not making any favourites with the team and they are singing and wasting time preparing banners. "They have to concentrate on supporting the team, that's what they have to do. "Every game they continue singing and preparing banners, they are wasting time. What they have to do is support the team. "I am a professional and I am doing my job. What I want to do is win every single game for Chelsea." Reports emerged from Stamford Bridge earlier in the week that Benitez was involved in a heated exchange with members of his squad after their 2-0 defeat at Manchester City on Sunday. Before the FA Cup tie with Middlesbrough, Benitez insisted he had a "fantastic" relationship with the club's players. He reiterated his satisfaction with his squad after they set up an FA Cup quarter-final clash with Manchester United. "I have a top side and a good group of players who work hard and it is a top club, it is not a problem," he said. "The problem is a group of people who can say what they want." Chelsea have won 13 of 26 matches since Benitez took charge and are fourth in the Premier League, 19 points behind leaders Manchester United. The former Inter Milan boss said he would be "the happiest man in the world" were the club to qualify for the Champions League, but questioned the decision to call him 'interim manager'. "I have a title. Someone decided the title would be interim. Why? Just in case?" said Benitez. "Fine, that is your decision. I don't agree, but that is your decision and now everybody has to take responsibility. "Everybody is interim because after you there is another one. In this case they didn't have anyone so why did they put interim? "I can't change the titles and the perception so it doesn't matter now. What I have to do is be sure that I give 100% every single day. They will know I am trying to do my best. "The manager is the manager. One month, three months, seven months - it doesn't matter. "I think the reason why the group of fans is not happy is because I was Liverpool manager, we played in the Champions League, massive games, that's it."