The Brazilian is believed to have picked up the disease while travelling, but the club hope that he is the only player infected by the illness
The 21-year-old moved to the AWD Arena in January for €1.3 million from Criciuma, and it is believed he picked up the illness while traveling between the two countries.
"We are very sorry for Franca but the most important thing is that he recovers and returns healthy," sporting director Jorg Schmadtke said in a club statement.
"After treatment he will continue his career as a footballer according to the doctors. That is important and good news for him and us."
Hannover are hopeful that none of their other players have the virus, but will conduct blood tests with the squad to be on the safe side.
Franca is yet to make his debut for H96 since his move last month.