"He is going to play," Guardiola said. "The doctor told me at the beginning of the week there was a doubt about him playing that's why I said what I said but today he arrived and said he is really good so he is going to play."
City are eight points above their neighbours and are yet to lose a league game this season but Guardiola says that his team will need to be at their best.
"My focus is going there, relax and knowing that if don't do our best it will be almost impossible to beat them and try to play good football," he said.
"It's an important game because it is against Man United, you can get points and the other cannot but it's the same for them.
"It's a marathon, the Premier League. We haven't arrived at the half of the marathon so there are a lot of points to play."