Thiago Alcantara has contracted COVID-19.
Liverpool confirmed the news on Tuesday evening after the midfielder missed the 3-1 win over Arsenal for unspecified reasons.
The Premier League champions say the 29-year old "has exhibited minor symptoms" but is in good spirits and getting better.
Under UK government guidelines, Thiago is required to isolate for a period of ten days.
During Liverpool's victory at Anfield on Monday night, the Premier League confirmed that ten individuals had tested positive for coronavirus in their latest round of screening.
Thiago Alcantara has tested positive for COVID-19 and is currently self-isolating according to the necessary guidelines.
The club has, and will continue to follow, all protocols relating to COVID-19 and Thiago will remain in self-isolation for the required period of time.
— Liverpool FC (@LFC) September 29, 2020
It was already known that three of those positives - David Moyes, Josh Cullen and Issa Diop - were at West Ham.
Liverpool first-team doctor, Dr. Jim Moxon, said. “It is the choice of each individual whether they reveal publicly the outcome of a COVID-19 test.
"We have followed all the protocols to the letter and Thiago is OK.
"He will be self-isolating now as per the guidelines and hopefully he’ll be back with us soon.”
Thiago will miss Sunday's trip to Aston Villa, but it's hoped he'll return in time for the Merseyside derby at Goodison Park on October 17.