The 27-year-old midfielder admitted he was operating at only 70 percent of his best during Leverkusen's 2-0 Bundesliga win over RB Leipzig before the international break.
"I'm not at 100 percent yet. Against Augsburg, I was at 60 percent, and against Leipzig, I was already at 70 percent," Diaby told Bild.
Diaby returned to Leverkusen in the European summer from Saudi Arabian club Al-Ittihad and has been working his way back towards full fitness.
The international break has given the France international an opportunity to improve his physical condition before Leverkusen's next Bundesliga fixture.
Despite admitting he is not yet at his best, Diaby has been pleased with his contribution since returning to the club.
"I played well and helped the team, but I know I can play much, much better," he said.
Diaby will now look to take another step forward when Leverkusen return to Bundesliga action away to Mainz on October 10.
Jurgen Klopp was left encouraged by Germany's performance in his first match as head coach, despite seeing his side concede a late equaliser in a 1-1 draw with the Netherlands in the UEFA Nations League on Thursday.
Dani Olmo's agent has welcomed reports of interest from Bayern Munich, but the Barcelona midfielder remains focused on fighting for his place at the Catalan club.
Cody Gakpo struck in the 92nd minute to deny Jurgen Klopp a winning start as Germany head coach, with the Netherlands rescuing a 1-1 draw in Amsterdam.
Harry Kane has revealed he is seriously considering a move into the NFL later in his career, with the England captain believing his experience taking penalties could help him make the transition.
