Mahrez and Laporte both returned positive tests for coronavirus despite not showing symptoms and are now isolating.
"Manchester City FC can confirm that Riyad Mahrez and Aymeric Laporte have tested positive for COVID-19," the club said in a statement on Monday.
"Both players are currently observing a period of self-isolation in accordance with Premier League and UK Government protocol on quarantine. Neither is displaying symptoms of the virus.
"Everyone at the Club wishes Riyad and Aymeric a speedy recovery ahead of their return to training and the new season."
City kick off their Premier League campaign against Wolves on Sept. 21 after being granted an extended break following their run to the quarterfinals of the Champions League.