"Coach Popovich has been in our restaurant in the past multiple times," Smithe told mysanantonio.com.
"We don't discuss anything that goes on when VIPs are in the building."
While it's difficult to verify whether Popovich was definitely the man who left the generous tip ahead of game four of the playoffs, which Memphis won 110-108 in an overtime classic, US media is reporting the handwriting on the bill appears to match that of the 68-year-old.
That the Spurs played the Grizzlies at their home stadium FedEx Forum, which is just a few blocks away from McEwen's, on April 20 and 22 also adds weight to the theory Popovich is responsible for the donation.
According to a Twitter user, the Spurs mentor also reportedly left a $1000 tip in April 2016.