The reigning champions found themselves down near the relegation zone after stuttering badly in the first part of the season but have since picked themselves up to currently occupy 10th place on the table following the December arrival of Guus Hiddink.
Regarding Chelsea's woes, which have potentially cost them European football for next season, goalkeeper Courtois suggests the squad was not up to it when the season kicked off but is happy things have improved in 2016.
"I think our pre-season (with Chelsea) was too short," the 23-year-old told RTBF.
"Physically, we weren't ready. We lost our first game in the Community Shield, then we needed a change, and Guus Hiddink's arrival did us some good.
"Europe? It'll be hard, but we're going to try and finish the season strongly."
Courtois is currently with the Belgium squad ahead of their proposed friendly with Portugal on March 29 which could now be cancelled following the terrorist attacks in Brussels.