Display Screen or Portion Thereof with Transitional Graphical User Interface

FIG. 1 is a first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design, according to a first embodiment;

FIG. 2 is a second image thereof; and,

FIG. 3 is a third image thereof.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1 to 3 . The process or period in which one image transitions to another forms no part of the claimed design.

The outer perimeters illustrated by broken lines in the figures depict a display screen or portion thereof and form no part of the claimed design.