Display Screen or Portion Thereof with Transitional Graphical User Interface

FIG. 1 is a front view of a first image in a sequence of a display screen or portion thereof with transitional graphical user interface in accordance with my new design;

FIG. 2 is a second image thereof; and,

FIG. 3 is a third image thereof.

The outermost broken line rectangle shows the display screen or portion thereof and forms no part of the claimed design. All other broken lines show portions of the graphical user interface and form no part of the claimed design.

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