Display screen or portion thereof with transitional graphical user interface

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

FIG. 2 is the second image thereof;

FIG. 3 is the third image thereof;

FIG. 4 is the fourth image thereof;

FIG. 5 is the fifth image thereof;

FIG. 6 is the sixth image thereof;

FIG. 7 is the seventh image thereof;

FIG. 8 is the eighth image thereof;

FIG. 9 is the ninth image thereof;

FIG. 10 is the tenth image thereof;

FIG. 11 is the eleventh image thereof;

FIG. 12 is the twelfth image thereof; and,

FIG. 13 is the thirteenth image thereof.

The outer perimeter shown in broken lines illustrates a display screen or portion thereof and forms no part of the design; the remaining broken lines illustrate portions of the transitional graphical user interface that form no part of the design.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1 - 13 . The process or period in which one image transitions to another image forms no part of the claimed design.