The Belgium international has featured in every minute of Atletico's La Liga campaign, conceding only 11 goals, helping Diego Simeone's men to second, level on points with leaders Barcelona.
Garcia, who found the net in Atletico's 2-0 Copa del Rey win over Valencia, says the Chelsea loanee is playing a crucial role for the club.
"Courtois brings a lot to the team and his self-belief helps us wins games," Marca quotes him as saying.
"It's not just our goalscorers who're important; he is too."
The 21-year-old is in his third season on loan at the Vicente Calderon with Petr Cech preferred as No.1 at Stamford Bridge.
However, Garcia is confident Courtois will continue to improve, highlighting his maturity as a major advantage.
"He's young, but he's tremendously mature for his age," he continued. "Keepers usually reach that level when they're slightly older.
"He also has room to improve and what's good is that he wants to work on becoming a better keeper."