Two Benfica players have been taken to hospital after their team bus was attacked following their first behind-closed-doors match.
German Julian Weigl and Serbian Andrija Zivkovic were hit with shrapnel and taken to hospital as a precaution.
Portuguese champions Benfica missed the chance to move clear of title rivals Porto at the top of the table after being held 0-0 by Tondela.
Fans had gathered to support the team outside Benfica's Estadio da Luz.
The attack occurred on a major motorway between the stadium and training ground.
"Benfica denounce and lament the criminal stoning the bus of its players was victim to," a Benfica club 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."
The top two in the primeira liga table are now level on 60 points with nine rounds of matches remaining.