San Antonio Spurs legend Gregg Popovich left a local restaurant in an ambulance Tuesday night ... after officials say they received a call for an elderly person who had "fainted" while eating dinner, TMZ Sports has learned.

We've obtained video of the 76-year-old on a stretcher as he was placed into the back of an emergency vehicle outside a San Antonio steakhouse around 8:20 PM.

Our sources tell us Popovich appeared to still be dealing with the effects of the mild stroke he suffered in early November while at the establishment ... and was there for close to two hours before suffering the medical emergency.

Officials say they responded to the scene after receiving a call for an elderly person who had fainted ... and the patient was taken to the hospital with non-life-threatening injury or illness.

Another source tells us Pop was alert and talking by the time he entered the back of the vehicle ... and he is now back home and doing better.

Popovich has taken a step back from the Spurs to focus on his health ... with assistant Mitch Johnson serving as interim head coach in his absence.

It was announced in February he would not return this season.

Popovich is widely considered one of the greatest basketball coaches of all time ... leading the Spurs to five NBA Finals championships and Team USA to a gold medal at the 2020 Olympics in Tokyo.

He is the winningest coach in NBA history.