Arsenal have confirmed they are investigating whether academy coach Mark Arber bet on the signing of Mesut Ozil.
It has been reported that Arber posted a tweet on his personal account on Monday admitting he had bet on the German international midfielder's club-record £42.4m move from Real Madrid.
"We take this very seriously," said a club spokesman.
"All Arsenal employees and workers are well aware of their responsibilities in this respect and we are looking into this as a matter of urgency."
Football Association betting rules do not allow people to bet on any events involving their own club.