A bus carrying the Benfica football team was stoned on Thursday, breaking the glass and injuring two players, after they had played their first game since the coronavirus halted the season, the club said in a statement.
The attack on a major motorway between the club's Estadio da Luz and training ground followed Benfica's first game in three months after the season was disrupted by the COVID-19 pandemic.
"Sport Lisboa and Benfica denounce and lament the criminal stoning the bus of its players was victim to," the statement read.
"We guarantee total collaboration with authorities to whom we appeal for the greatest effort to be made in identifying the delinquents responsible for these criminal acts."
In a separate statement the Primeira Liga added: "Liga Portugal strongly condemns the cowardly attack in which the Benfica squad was targeted tonight after playing CD Tondela... It is absolutely unacceptable that events like these continue to take place in society, it's important to make clear that the perpetrators of these acts are not football fans, but criminals who will be identified by the security forces and held responsible."
Portuguese champions Benfica missed the chance to move clear of title rivals Porto at the top of the table after being held to a 0-0 draw by lowly Tondela. The top two are now level on 60 points with nine rounds of matches remaining.
Fans had gathered outside the gates of Benfica's stadium in Lisbon to support the team because restrictions imposed due to the coronavirus outbreak prevented them entering the ground.