The Argentine Coach spent five years at Stamford Bridge during his impressive career that saw him having stints for both AC Milan and Inter Milan.
The Blues took to twitter to send their well wishes for the former player with a simple message and photo.
The striker won his first European League trophy at Chelsea in the 2005/06 season under Jose Mourinho after returning from his loan to AC Milan.
The current Al-Duhail manager also helped the Blues to win the Community Shield that season as well for the first time since 2000.
The forward saw success in Italy as well, winning the league three times in his tree years at Inter Milan.
Since retirement, Crespo has managed six clubs, including Sao Paulo as well as Italian and Argentinian teams.
In his time in charge, the 47-year-old continued adding to his trophy cabinet, including winning the Campeonato Paulista with Sao Paulo in 2021.
Fans in the comments were quick to wish the star a happy birthday, as well as look back on significant times in the player's career.
One commenter said, "Remember his 92nd minute goal against Wigan?"
Another replied, "Those were the days. When we could sign whoever we wanted."
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