It's said Courtois is keen on a move to the Santiago Bernabeu Stadium and is knocking back Chelsea's offers regarding a new contract, as the 25-year-old reportedly "feels that his time in the Premier League is coming to an end."
Flanagan also noted how Los Merengues have been impressed by Courtois since his first stint in Spain's top flight—a three-year loan spell with capital rivals Atletico Madrid in which he won UEFA Europa League, Copa del Rey and La Liga trophies.
Courtois developed into a star with Los Rojioblancos, and now Real appear keen on him replacing 30-year-old Keylor Navas. As noted by Flanagan, the Blues could be tempted to sell Courtois next summer if no new contract can be agreed, instead of seeing him leave for free in 2019.
However, losing Courtois, especially on a free transfer, would be a huge blow for Chelsea, since the Belgium international remains one of the finest stoppers in England's top flight. Consistency is the key to Courtois' game, as he rarely makes mistakes or gifts goals away.
The 25-year-old is also commanding in the air and quick and agile on the deck. Those attributes make Courtois a fine shot-stopper, as well as a powerful and confident presence when dealing with crosses and high balls into the box.
Courtois' qualities have helped him enjoy similar success with Chelsea as he did with Atleti—the Belgian has won two Premier League titles and a League Cup with the Blues.
Given his performances, interest from Real makes sense, but Chelsea should do all they can to keep the gifted 'keeper around for longer.
It's not as if Chelsea boast a natural successor. Asmir Begovic is no longer around as a replacement in waiting, and 36-year-old Willy Caballero is the Blues' primary back-up.
Since they will struggle to find a goalkeeper as talented elsewhere, Chelsea would be wise to continue making Courtois contract offers good enough to eventually convince him to extend his stay at Stamford Bridge.