The French defender's status was announced after COVID-19 tests carried out among the Barca squad on Friday (AEST).
Umtiti is asymptomatic and isolating at home, the club revealed, and the centre-back was already certain to miss the UEFA Champions League quarter-final thrashing against Bayern Munich.
The 26-year-old, who has made just 18 appearances in all competitions in the 2019-2020 season, had not travelled with his team-mates to Lisbon because of a knee injury.
"After the PCR tests carried out [on Friday AEST], the first-team player Samuel Umtiti has tested positive for COVID-19," a Barcelona statement read.
"The players is asymptomatic, is in good health and isolating at home.
"The club has informed the relevant sporting and health authorities, as well as tracing all the people who have had contact with the player so that they can undergo the corresponding PCR tests."
With Umtiti unavailable, compatriot Clement Lenglet was chosen to start alongside Gerard Pique at the heart of Barcelona's defence for the clash with Bayern, and was at fault on several occasions as Bundesliga champion cruised to an unbelievable 8-2 victory.