The Belgian international had joined the English Premier League side last summer from Atletico Madrid. Courtois, speaking to Spanish daily Marca, has said that when he left La Liga he had promied to himself to return to the league one day.
Marca quoted Thibaut Courtois: "When I left Spain I had it clear in my mind that one day I was going to return there.
"I have a contract with Chelsea for three more years. In 2018, when I enter the final year of my contract, we will have to evaluate if it is better to renew or walk away."
Earlier this season, it was speculated that the Belgian custodian would leave the club. Chelsea were considering Southampton goalkeeper Fraser Forster as a possible replacement.
Later, manager Antonio Conte somehow managed to convince the goalkeeper to stay back at the club.
Since last season, La Liga giants Real Madrid are in search of quality goalkeeper who would serve the club for longer period of time.
Courtois further stated: "When I injured my knee they sent me a fax wishing me a prompt recovery."
It is being reported that Real president Floretino Perez is a key admirer of Thibaut Courtois and he might soon enquire with the Blues for the goalkeeper's availability.