Paris Saint-Germain coach Thomas Tuchel's options are depleting ahead of the Champions League round-of-16 second leg against Borussia Dortmund next month.
Dortmund lead 2-1 after last week's opening leg and an Erling Haaland brace, although Neymar's away goal gives the Ligue 1 leaders hope of reaching the quarterfinals.
According to the French champions' latest medical update, Herrera will miss 6-8 weeks of action with a left thigh problem, and Silva will only be able to return from his right thigh issue in three weeks -- depending on how the injury evolves.
Assuming that both prognoses are correct, the pair will miss the return leg with Dortmund at Parc des Princes, meaning that Tuchel already has four players that he cannot count on for the crunch clash.
Abdou Diallo is currently working his way back to fitness, so could boost the German tactician's defensive options, but Colin Dagba has been out for some time and is not certain to be fit and ready for Lucien Favre and his men.
It has been a period filled with bad news for Tuchel since the loss at Dortmund. An ill-timed birthday party for Edinson Cavani, Angel Di Maria and Mauro Icardi led to leaked footage of the players partying while and Neymar received a red card in Sunday's 4-3 Ligue 1 win over Bordeaux.
Although it was a return to winning ways, it was a sixth match without a clean sheet -- a run that has seen PSG ship 13 goals.
Despite Neymar's unhappiness at being kept safe in the lead-up to the opening leg in Germany, he will miss at least one domestic fixture through suspension and could miss more if the ban is extended.