Benfica have vowed to help authorities find the perpetrators who stoned the team's bus in an attack that left Julian Weigl and Andrija Zivkovic requiring hospital treatment.
The vehicle was targeted when travelling down a major motorway following Benfica's goalless draw with Tondela at Estadio da Luz on Thursday.
It was a game that marked the team's resumption in the Primeira Liga following the suspension of domestic football in Portugal due to the coronavirus pandemic.
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Supporters had earlier gathered outside the stadium in Lisbon as games are being played behind closed doors due to protocols being put in place to limit the spread of Covid-19.