New head coach Carles Martínez's preference is for a fast, attack-minded option on the left, and two names have emerged as the primary candidates.
The first is Raphaël Guerreiro, the free agent full-back released by Bayern Munich this summer. The 32-year-old Portuguese international is similar in profile to Grimaldo — technically accomplished, left-footed and capable of playing in either a back four or wing-back role.
Bild reports that Guerreiro is a genuine option and that salary would not be an obstacle. The complication is age and the head coach's preference for a younger, more dynamic profile.
That points toward Arsène Kouassi of Lorient. The 22-year-old fits Martínez's specifications more closely — quick, aggressive in transition and still developing. A fee of around €20 million is reported. Kouassi represents Burkina Faso internationally and already has an international connection to Bayer Leverkusen's squad through teammate Edmond Tapsoba.
He is also being tracked by VfB Stuttgart and Eintracht Frankfurt, meaning Leverkusen will face competition if they move formally.
On the right side of defence, Leverkusen have identified Konstantinos Mavropanos of West Ham United as a target. The Greece international centre-back, 28, can operate at right centre-back in a back three or as a right-sided defender in a four.
West Ham's relegation makes him available, and Borussia Dortmund have also been linked. Sergiño Dest of PSV Eindhoven is listed as an alternative for the right flank, though Bayern Munich are monitoring the United States international simultaneously.
Leverkusen's challenge is that Grimaldo was not simply a left-back — he was one of the best players in the Bundesliga across his two seasons at the club, central to the title-winning campaign of 2023-24. Finding a direct replacement of that quality at short notice is a genuine problem, and the club will need to act decisively before preseason begins.