Alonso will tackle the Saudi Arabia-based event at the wheel of a factory-run Toyota Hilux with Dakar motorcycle legend Marc Coma as his co-driver.
Since August, the two-time Formula 1 world champion has been ramping up his preparations for the marathon, contesting the Lichtenburg 400 in South Africa, the Morocco Rally and Al-Ula Neom Rally in Saudi Arabia, in which he secured third place overall.
More recently he completed 600km of testing in the Abu Dhabi dunes earlier this month, his final run before the start of the Dakar on January 5.
Alonso has maintained that he doesn't expect to fight for the win and will primarily focus on making it to the finish of the two-week event.
But, speaking to Motorsport.com, Castera said Alonso could realistically aim to fight for a stage victory in the second week of the Dakar, once he's gained more experience.
"He has to learn to be humble, because if he wants to advance to the maximum level he has to accept being behind slower drivers than him in theory," he said. "That is the first thing.
"But I think he can win a stage before the end of the Dakar, in the second week he can do something special. But he will have to wait and take the first week step-by-step.
"Then, I think he will have the chance, especially with Marc, who knows the rally very well and everything, which will help him a lot."
#205 Toyota Gazoo Racing Toyota Hilux: Fernando Alonso