So it's officially a love triangle at Chelsea.
But it is understandably difficult for a man who held the no.1 spot for the best part of 10 years to settle for second best.
Varying reports suggest 32-year-old Cech is either A) leaving Stamford Bridge of his own accord B) wanted by other clubs, or C) being pushed to leave by the club itself.
Very few, then, would blame the Czech shot stopper for wanting to part company with the Blues this summer.
Could Mourinho, however, have an understanding with the veteran that others are not yet aware of?
It would be unlike the 'Special One' not to have a plan of action for such events, of course, with the Portuguese coach known chiefly for his man management and ability to form strong bonds with his players.
Surely, then, there must be some sort of compromise that isn't leaving things to chance.
Mourinho has said that Courtois is his number one for now and for his next game - but not for the rest of the season. So why not sort things by competition?
Much like the Iker Casillas/Diego Lopez paradigm at Real Madrid last season, the 51-year-old could use Cech's experience and expertise in the Champions League and FA Cup, possibly Capital One Cup too.
After all, while the Premier League title is a priority for Chelsea, Mourinho cannot risk placing all his eggs into one basket. Other trophies are there for the taking, while European progression is a must.
Using them could be the Blues boss's best way of keeping Cech at the club, allowing the 32-year-old to maintain his previous level of responsibility and keeping a top-class goalkeeper at the ready should Courtois get injured, anyway.
It's either that or say goodbye to yet another club legend.