4:38 PM PT -- A rep for Carlos Santana tells TMZ ... tonight's concert at the Majestic Theatre in San Antonio has been postponed. The singer is currently under observation in Texas. His rep says he's doing well and looks forward to coming back to San Antonio soon as well as continuing his US Tour.

The rep adds the San Antonio show will be rescheduled soon.

Health scare for Carlos Santana ... he's in a hospital right now getting treatment after suffering a medical emergency before a concert in Texas ... TMZ has learned.

A rep for the legendary musician tells us Carlos suffered a medical emergency Tuesday that they suspect is dehydration. He was put into an ambulance and has left the venue, and we're told by his rep he's been hospitalized for further testing.

Santana's rep says his Tuesday night show at the Majestic Theater in San Antonio is not currently canceled -- but that could change depending on how Carlos responds to treatment.

Folks who were there say Carlos was doing a sound check when he suffered an emergency and had to be taken out of the venue on a gurney and placed in the back of an ambulance.

A similar incident played out a couple years ago, when Santana collapsed onstage in July 2022 from what his team claimed was heat exhaustion and dehydration. In that instance, Carlos was in the middle of his show and he had to be taken to a hospital.

So far, that hasn't happened here.

Carlos also has shows scheduled for Friday, Saturday as part of his Oneness Tour 2025.

Story developing ...