The Spanish international has joined for the rest of the 2021/22 campaign and the Blues have option to buy the midfielder, reported to be in the region of £30million.
The deal sees the Blues add some crucial depth to their midfield of N’Golo Kante, Mateo Kovacic and Jorginho, and proven quality with Saul capped 19 times for Spain.
The 26-year-old appears hungry for a new challenge, having fallen out of the La Liga champions starting XI, after making 340 appearances over the course of his time at Atletico Madrid.
He told the official Chelsea website: “I am very excited to start this new challenge with Chelsea. Blues fans, I am one of you now and I can’t wait to wear the shirt, start training and see all of you. See you soon!”
The loan sees Marina Granovskaia pull off another impressive deal, with Atletico Madrid initially making the deal contingent on an obligation to buy and the transfer guru is pleased to have landed a star with such calibre.
Chelsea director Granovskaia added: “We welcome Saul to the club and believe he completes our squad as we compete for honours in five different competitions this season.
“He is a proven winner, a player with huge experience and we know he will be very well-suited to the challenges that face us on all fronts in the coming year.”
Saul’s debut could come against Aston Villa at Stamford Bridge on September 11 following the international break.