For the last decade, Cech has been number one at Chelsea, helping the club win three Premier League titles, four FA Cups, two League Cups and the UEFA Champions League.
However, the Czech Republic international has been displaced by Courtois this season, after the Belgian was recalled to Stamford Bridge following three years on loan at Spanish champions Atletico Madrid.
Cech recently voiced his concerns at not being the club's first choice keeper, and Courtois too believes his rival is too good to be warming the bench.
"As a goalkeeper you want to play. If I was in that situation where I didn't play a lot, then I would leave too," he told Sky Sports.
"I think Petr is still a goalkeeper with a lot of quality and one of the best there is."
Courtois has played his part in helping Chelsea go unbeaten in the opening 11 Premier League matches, but he feels it will be tough to emulate Arsenal's 'Invincibles' side of 2003-04, who went the entire campaign without losing a league game.
"Obviously a lot of people hope that we can go unbeaten, we will see," he added. "The Premier League is a very hard competition, so I think that's maybe why just one team did it, but I think it will be hard.
"It's more important to be champions, and if it is unbeaten then okay."
