Sambia, who has been hospitalised since Tuesday and was placed in an artificial coma, is the first confirmed case of a Ligue 1 player testing positive for the virus.
"His condition is stable this Friday. It has not deteriorated, nor improved," agent Frederic Guerra told Le Parisien about his client's status. "It is tough. He really respected confinement. He did everything well. He must have contracted the virus while shopping.
"He suffered three days of severe diarrhea -- like gastroenteritis. Then, on Tuesday morning, he went to the hospital. I reached him when he was on an IV. He had just received the COVID-19 test result. This one was negative. He was due to leave on Wednesday, then his condition worsened with his lungs.
"It grew more complicated in transit. He went back to the same hospital, then he changed hospitals twice before being placed in an artificial coma."
It was at the subsequent hospital that Sambia was tested again. Montpellier had released a statement on Thursday saying one of their players had been hospitalised but didn't mention Sambia nor that it was due to COVID-19.
Football in the country has been suspended indefinitely amid the outbreak although French Football Federation president Noel Le Graet proposed a return to action in June.
A restart for Ligue 1 had been provisionally set for June 17, but Le Graet conceded it would depend on government approval.
ESPN's Jonathan Johnson contributed to this report.