The San Antonio Spurs players surprised the 7'4" rookie right on the court ... surrounding him and breaking out the classic tune.

Wemby clearly wasn't expecting it ... but jumped right into singing and clapping with his teammates.

"Hip hip hooray!" the players yelled after the song. "Hip hip hooray!"

Wembanyama also got another nice present on his birthday -- it was announced he's received over 221k votes to participate in the 2024 NBA All-Star Game so far.

To compare, that's more entries than Karl-Anthony Towns, Chet Holmgren and Kristaps Porzingis.

The first-overall pick of the 2023 NBA Draft has been getting a lot of love since he started his career ... in fact, his dunk on December 31 is on the verge of becoming the most-watched video ever on the league's Instagram page with 88.8 million views.

Wemby -- who's averaging 18.9 points and 10.2 rebounds per game -- also set several NBA records before his 20th birthday, including surpassing Dwight Howard for the most consecutive games with a double-double (8).