"Of course everyone knows he's here. I can't hide that — the photos are out there. Right now we're still working to finalise everything, including the medical. I'd rather talk about him officially once everything is done," Martínez said.
He ruled out any prospect of Diaby featuring this weekend regardless of how quickly the paperwork is completed.
"I think it's very difficult for him to already be part of the group. I can say he won't be in the squad on Saturday. Right now the most important thing is that everything gets finalised and Moussa can become part of our squad," the head coach said.
The fee is reported to be less than €30m for the 27-year-old, with an official announcement expected as soon as Friday.
Diaby previously spent two seasons at Leverkusen before leaving for Aston Villa in 2023, going on to join Al-Ittihad in Saudi Arabia the following year, where he won the domestic league and King's Cup during two productive seasons in the Gulf.
His return also draws a line under one of the more convoluted sagas of the closing transfer window, with Al-Ittihad having initially resisted sanctioning his exit while they searched for a replacement, reportedly eyeing Eintracht Frankfurt's Ritsu Doan before eventually relenting.
Leverkusen's own business elsewhere has continued in parallel: Ernest Poku and Exequiel Palacios are both closing in on departures of their own, with the club balancing fresh investment in attack against outgoing sales as the deadline approaches.