Hammers boss Slaven Bilic was preparing to take Reid off before the clash and claimed he missed it.
He said: “I didn’t see it at all. We were preparing to make a substitution so I didn’t see that and I didn’t react.”
City defender John Stones went off in the 58th minute with what looked like an eye injury. But Guardiola does not believe it is a serious problem.
Samir Nasri made his first appearance of the season when he came off the bench and almost scored twice.
Guardiola says it is up to the France midfielder if he wants to stay beyond Wednesday’s transfer window closing.
The City boss added: “His quality is on another level but it depends on him. If you want to help us, want to stay, want to be part of something, it depends on him, not me.”