Tom Brady was asked to leave a park in Tampa that is closed because of the coronavirus pandemic after being found exercising alone by patrol staff.
The six-time Super Bowl winner joined the Tampa Bay Buccaneers in March after 20 years with the New England Patriots.
Tampa mayor Jane Castor said the quarterback, 42, was seen during a routine patrol of the park in Florida.
"A staff member saw an individual working out in one of our downtown parks," said Castor.
"She went over to tell him it was closed and it was Tom Brady."
Brady is regarded as one of the greatest players of all time, having won the Super Bowl more times than any other player - in 2002, 2004, 2005, 2015, 2017 and 2019.
He has made a total of nine Super Bowl appearances and been named the championship game's most valuable player (MVP) four times - both NFL records.
The City of Tampa messaged Brady on Twitter after Castor revealed the news during her daily coronavirus update on Monday.
"Sorry Tom Brady - our Tampa parks and recreation team can't wait to welcome you and our entire community back with even bigger smiles," it said.
"Until then, stay safe and stay home as much as you can to help flatten the curve."