Police Scotland are investigating claims that Celtic striker Leigh Griffiths sent “inappropriate messages” on social media.
Officers are trying to establish whether any criminal offence has taken place.
A Police Scotland spokesperson said: “We have been made aware of social media content. We are making enquiries and assessing for criminality.”
Griffiths has left Celtic’s pre-season training camp in Wales while the club looks into the matter.
A Celtic spokesperson said: “We have been made aware of online comments concerning Leigh Griffiths. The club will now look into this matter carefully.
“Leigh has left the club’s training camp as we do this.
“It would not be appropriate to make any further comment at this time.”
Celtic announced last week that Griffiths has signed a new one-year contract with the club.
The forward’s existing contract expired this summer and there had been speculation about his future as new Celtic boss Ange Postecoglou revamps the squad.
Griffiths only started eight games for Celtic last season as the team lost their grip on domestic trophies.