Two players were injured when a bus carrying the Benfica squad was stoned on Friday (AEST), after the team's goalless draw with lowly Tondela.
German midfielder Julian Weigl, 24, and Serbian winger Andrija Zivkovic, 23, were taken to the Hospital da Luz in Lisbon to be treated for injuries as a precaution, broadcaster RTP said.
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.
The draw meant Portuguese champions Benfica missed the chance to move clear of title rivals Porto at the top of the table.
The top two are now level on 60 points with nine rounds of matches remaining.
Benfica issued a statement later, promising to track down the offenders.
"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."