Leicester and Crystal Palace also had scouts at the game, with the Foxes weighing up a bid to reunite him with countryman Riyad Mahrez next summer.
But Spurs, who have been following Slimani since the 2013 Africa Cup of Nations, are understood to retain the biggest interest in the player.
Slimani, who also starred for his country at the 2014 World Cup in Brazil, has four years left on his contract.
But it is understood he could be set for a move in the summer if a club meets his £23m release clause.
Spurs have been forced to rely heavily on Harry Kane for goals this season and are looking to add more firepower to their squad.