Arsenal are well stocked for defenders in each position but it appears that new head of recruitment Sven Mislintat is keen to make his mark at the Emirates Stadium.
According to RMC Sport, Arsenal have already made an approach to sign the 21-year-old, but the German outfit are said to be reluctant to sell during the January window.
However, it has been claimed that Mainz could be willing to do business for the right price at the end of the campaign, once Diallo has completed a year at the club.
The Frenchman - who was previously at Monaco - has scored twice in 15 appearances in the Bundesliga during the current campaign.
In the summer, Arsenal will require a replacement for Per Mertesacker, who will end his playing career and take a leading role with the academy.