Armindo Sieb is currently on loan to Mainz from FC Bayern. It was confirmed in the summer that Mainz has secured a purchase option. To retain Sieb permanently after the loan ends in 2026, Mainz would need to pay an additional five million euros to Bayern, in addition to a one million euro loan fee. Despite some fitness deficits, Sieb is considered by many to be a potential bargain for Mainz, having been a two-time U21 national player and a notable performer with 15 appearances this season. However, Bayern retains a buy-back clause, which is expected to be higher than Mainz's purchase option.