When the Rebbe was living in berlin he received his smicha from Rabbi Yechiel Yaakov Weinberg (known as the Seridei Eish after the name of his sefer).
Kowalski says that the Seridei Eish told him that the next day, he tested the young scholar and “was shocked by the great knowledge of all that it said in his booklet, and even more than was written there. He immediately gave Rabbi Menachem Mendel Schneerson rabbinical ordination.”
In a recent conversation with Kowalski in Zurich, he clarifies how it came about that he discussed this with the Seridei Eish. “I was a student of the Seridei Eish in Montreux, Switzerland,” he says, and one day he was speaking to the Seridei Eish and asked: “Why don’t you have contact with the Lubavitcher Rebbe?”
The Seridei Eish said: “I will tell you the truth: he was my student, and now he is Rebbe. If I would write to him, I would need to write to him [the honorific titles] harav hagaon, hatzadik. I cannot write like this to a student, and to write to him without saying this is not respectful because he is a Rebbe. So, I do not write.”
Another student of the Seridei Eish, Rabbi Yosef Tzvi Dunner, who headed the Union of Orthodox Hebrew Congregations in London, told his son and grandson shortly before he passed away that “he remembered [the Rebbe] well,” records his grandson Rabbi Pini Dunner. “The Rebbe stood at the back of Rabbi Weinberg’s shiur [class], and would talk in learning after almost every shiur.”