Chelsea have signed a lot of players in the last two seasons and they are far from done. Reports suggest the Blues are looking to add Jules Kounde and Saul Niguez to their squad before the window closes this month.Thomas Tuchel has a ton of fresh faces in the squad and Chelsea have one of the youngest teams in the Premier League. However, there are a few players who have been at the club for a long time and are the backbone of the squad.On that note, here is a look at the5 longest-serving players in the current Chelsea first-team squadNote: Only time in the first-team squad has been calculated and time spent in the academy has not been counted. Additionally, Kurt Zouma has been left out as he's reportedly on the verge of completing a move to West Ham United.#5 Marcos AlonsoArsenal v Chelsea - Premier LeagueChelsea signed Marcos Alonso from Fiorentina back in August 2016 and his time at the club has been erratic. The Spaniard went from being the best left wing-back in the world to an average left-back with the flick of a switch.What a prediction, @marcosalonso03! 🥳Will he find the target again this weekend? Play Predictor for Arsenal is now open, with more top prizes on offer! 🙌— Chelsea FC (@ChelseaFC) August 20, 2021Marcos Alonso has enjoyed a good spell at Chelsea and given the start to the ongoing Premier League season, his time at the club is nowhere near its end. He has a contract until 2023 at Stamford Bridge and could sign an extension next summer if things go according to plan in the coming months.#4 N'Golo KanteArsenal v Chelsea - Premier LeagueN'Golo Kante has been at Chelsea since July 2016 and was one of the first signings under Antonio Conte. The Italian manager was keen on working with the Frenchman, who was on top of his game at Leicester City.Since then, N'Golo Kante has worked under Maurizio Sarri, Frank Lampard and Thomas Tuchel at Chelsea. Several players have gone in and out of the team but the Frenchman has remained a constant.Our first switch of the afternoon.On comes @nglkante! 💪🔴 0-2 🔵 pic.twitter.com/bbkxD4AcIA— Chelsea FC (@ChelseaFC) August 22, 2021Thomas Tuchel spoke highly of N'Golo Kante earlier this year and said:"For years, I was fighting to have him (Kanté) in my team and now we did it the other way around – I came to his team (Chelsea). It's a coach's dream to have N'Golo (Kanté) on your side, because he makes things easy for everybody on the pitch.""He (Kanté) is such a nice guy, such a humble person and his mentality is to be everywhere on the pitch, to make things easy, to help out, to win the ball back. I'm very, very happy that this kind of player shines so brightly suddenly, on this level of performances, because this is important for football that these kinds of players, who serve a team, are in the spotlight."Like Marcos Alonso, N'Golo Kante has a contract until 2023 and is set for fresh contract talks this season.