While the 26-year-old has not been formally suspended at this stage, his club have determined that he will not be considered for first-team duties until the matter is resolved. It is thought that Liverpool will request the testing of a B sample.
READ MORE | Liverpool sideline Sakho after failed drugs test
Sakho's participation at Euro 2016 is therefore in doubt, something that has left Paris Saint-Germain star and close friend Matuidi "very sad".
Speaking after PSG's Coupe de la Ligue final win over Lille on Saturday, Matuidi said: "I don't really know the full story, but it's true if Sakho wouldn't be selected for the Euros, I would be very sad.
"I consider him as a brother and I'll always support him.
"I know he is very professional, very honest, he's a warrior and I hope everything will go well."