Doku wasn't in Guardiola's team for Man City's win over FC Copenhagen in the second leg of the UEFA Champions League last 16 on Wednesday night.
This weekend, Man City will play Liverpool at Anfield in what could be the most important game of their season. At the top of the Premier League table, only one point separates the two teams.
A win over the Reds would put them on top and make them the clear favorite to win the title, ahead of Liverpool and Arsenal.
But they might not have Doku. Guardiola revealed why Doku couldn't play in Copenhagen before the game:
He said, "He had some muscle problems, so we didn't want to take the chance."
Doku missed eight games in December of last year because of a muscle issue.