What is the ruling on praying behind an Imam who believes that other than Allah can create or bestow offspring?

Supplicating to other than Allah is considered major shirk (polytheism), such as seeking help from a creature for something only Allah can do. Whoever does this is akin to the polytheists who took intermediaries between themselves and Allah. Whoever believes this is a disbeliever by the consensus of Muslims, and prayer behind him is not valid, due to Allah's saying: "If you associate [anything] with Allah, your work will surely become worthless, and you will surely be among the losers." The obligation is to replace this Imam, or pray in another mosque, or at home if that becomes difficult.