The Sweden international also missed out on the 2026 FIFA World Cup following delays in his recovery from a complex knee operation.
The 26-year-old has been involved in light training over the summer, alongside fellow returning star James Maddison, but De Zerbi is less confident over the Swede than Maddison.
"We have to manage Deki in the best way we can, but it's is a great thing for us because he's a good player and a good guy.
"He deserves to play again, and we have to work day by day, and also for Deki the international break is important in his rehab.
"He doesn't need my encouragement to keep working because he's strong-minded and a great character. He's an example for everyone.
"When he's at top condition and over the injury, he will be like another new signing. But, we don't have a date yet."