Sky Sports understands Celtic have made a bid for former Portugal Under-21 international winger Helder Barbosa from Sporting Braga.
The 25-year-old, who is a product of Porto's youth academy, joined the Archbishops in 2010, signing a three-year deal.
However, Barbosa is not thought to be in the plans of head coach Jose Peseiro this season and he is willing to let the player leave for the right price.
The left-winger, who scored twice in a 3-1 win against Birmingham City during last season's Europa League group game, has been linked with the Scottish giants during this summer's transfer window.
And manager Neil Lennon is keen to strengthen his squad ahead of their forthcoming Champions League campaign as they look ahead to taking on the likes of Barcelona, Benfica and Spartak Moscow in their group.