The 27-year-old Brazil-born Italy international, who can play at left-back or wing-back, joined the Blues from Roma in January 2018.
Emerson, a member of the Italy squad that won Euro 2020, made his 71st appearance for Chelsea as a substitute in their Premier League opener against Crystal Palace.
His time at Stamford Bridge has seen Emerson score a memorable late goal last season in eventual Champions League winners Chelsea's last-16 victory over Atletico Madrid. Prior to that, he provided an assist for Olivier Giroud in the 2018/19 Europa League final, where Chelsea beat Arsenal 4-1.
Emerson made four appearances at Euro 2020, winning the latest of his 19 caps as the Azzurri beat England on penalties in the final at Wembley.