Benfica manager, Jose Mourinho, will struggle with team selection against rivals FC Porto on Sunday, after a virus swept through his squad.
Several key players are believed to be down with illness.
According to Goal, Mourinho and some members of his coaching staff are even affected with symptoms.
This comes after a 1-0 defeat to Chelsea in the Champions League in midweek.
Mourinho, who recently revealed he had been suffering from a fever ahead of his return to Stamford Bridge, had dismissed his symptoms as a common flu.
However, current developments suggest a broader issue within the team environment.
The affected individuals are dealing with “headaches and body aches”, prompting concern within the club’s medical department right on the eve of the derby at the Estadio do Dragao.