Sechel, R’ Shach did not consider the Lubavitcher Rebbe to be a Gadol. He actually referred to him as “the madman who sits in New York and drives the whole world crazy”.
He said that the statements he made regarding his father in law being God clothed in a human body, just like Moshe, as kefirah, and said that Chabad followers were just like the followers of Shabtai Tzvi. When the Lubavitcher Rebbe was sick, R’ Shach said that he davened for him to recover, and also to do teshuvah for the path he followed.
He already accused the Rebbe of being a Mashiach sheker in the 1970s.
