Any process that stops, prevents, or reduces the frequency, rate or extent of the movement of proteins from the cytoplasm into the nucleus, and that occurs as part of the mitotic cell cycle spindle assembly checkpoint. In S. cerevisiae, this process involves inhibition of the karyopherin/importin Kap121p (also known as Pse1p), which acts as the specific nuclear import receptor for several proteins, including Glc7p. Glc7p functions in opposition to key spindle assembly checkpoint protein Aurora kinase (Ipl1p).