Is a raka'ah considered valid if you caught up with the Imam during sujud, but were unable to recite Al-Fatihah because the Imam bowed, or must you complete four raka'ahs?

It is not prescribed for a latecomer to recite the opening supplication (Du'a al-Istiftah) unless he catches the Imam while standing, and he knows that he can recite Al-Fatihah after the opening supplication before the Imam bows. Otherwise, he should prioritize Al-Fatihah because it is obligatory, and the opening supplication is supererogatory. If he catches the Imam in a state other than standing, he should not recite the opening supplication because its place is while standing, after the opening takbeer and before Al-Fatihah. If someone occupies himself with the opening supplication instead of Al-Fatihah until the Imam bows, and he is unable to recite it, then his prayer is invalid, and he must perform an extra unit (rak'ah) to compensate for the unit in which he did not recite Al-Fatihah, or repeat the entire prayer if he does not do so. This is according to the preponderant opinion regarding the obligation of Al-Fatihah for the congregant in every unit. However, according to the opinion that it is not obligatory for the congregant, his prayer is not invalidated.