The defender made his unofficial debut for the Gunners in an 8-0 win against National League side Boreham Wood and made a post on Instagram following the match.
Winger Dembele commented on the post, writing 'Grande Papa', which translates to 'Big Papa', a play on Papastathopoulos' name. The comment has led to some speculation that the player wishes to be reunited with his friend at Arsenal.
Though the comment is not an official confirmation and is purely speculative, it hasn't stopped Gunners fans getting excited about the potential signing of a new attacking option.
Arsenal have been linked to a number of wingers including Croatian star Ante Rebic and Portuguese winger Gelson Martins, and many supporters of the club appear to believe that a new winger would improve the club.
The London club has had a busy transfer window so far, signing at least five major players for their team, most recently 19-year-old midfielder Matteo Guendouzi from Ligue 2 side Lorient for around £8m.
New Arsenal boss Unai Emery does not look as though he intends to stop improving his side, and now that the World Cup has finished, the Spaniard is in a position to contact returning players and their clubs.
The Gunners have missed out on Champions League qualification for the last two seasons and the fans will be hoping that their five new signings can help them improve in the upcoming campaign.