The Blues are facing a battle to keep the Belgium international at the west London side ahead of the new Premier League season.
Courtois has been persistently linked with a move to the Champions League holders over the past few years.
The speculation has reached a crescendo this summer as the Chelsea FC number one looks to return to the Spanish capital.
The former Atletico goalkeeper is desperate to reunite with his two children in the Spanish capital from his relationship with his ex girlfriend.
Reports in England have suggested that Chelsea FC won’t sell Courtois before Thursday’s deadline unless the Blues can sign a replacement.
Asked whether current Real Madrid number one Navas would be a good replacement for Courtois at Stamford Bridge, Nicol said:
“If you are Chelsea, you have to look at the present and the future. The future isn’t Navas. He isn’t getting younger.
“Chelsea can’t get rid of one of their best players. Chelsea to get in the top four need a goalkeeper who can do it now and for the next seven or eight years. They don’t need an ageing goalkeeper.”
Courtois has won two Premier League titles, the FA Cup and the League Cup between 2014 and 2018 at Stamford Bridge.
The Belgian goalkeeper spent three seasons on loan at Atletico Madrid where Courtois won the La Liga crown, the Europa League and the Copa del Rey.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news