It is understood that a lot of clubs from across Europe had someone watch over the Liga NOS fixture, with Manchester United and Borussia Dortmund reportedly among them.
It is not clear which player in particular was being watched by Newcastle, but there is a good chance that Moussa Marega could have been someone under the microscope after he was reported to be a target on Tyneside in the summer transfer window.
A Bola reported in July that Newcastle were in the hunt to sign the Mali international, who started up front for Porto in their match against Vitoria.
Marega, 28, scored 21 goals and supplied 11 assists in 47 appearances across all competitions for Porto last season but unfortunately could not get on the scoresheet at the weekend when the Magpies had their man in the crowd.
He did assist one of the goals, but it could be worrying that a forward who has a massive £36.6million release clause is yet to score a goal in his first four outings of the new campaign.
Newcastle cannot be blamed for already having an eye on January’s transfer window.
It’s the lack of goals that could hurt Newcastle more than anything with just one goal, by Jonjo Shelvey, in their first two games so signing a forward like Marega could be something on their mind going into the winter.
However another goalless display in front of the Magpies scout could mean that their interest in him is cooling rapidly.