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;

FIG. 2 is a second image thereof;

FIG. 3 is a third image thereof;

FIG. 4 is a fourth image thereof;

FIG. 5 is a fifth image thereof;

FIG. 6 is a sixth image thereof;

FIG. 7 is a seventh image thereof;

FIG. 8 is an eighth image thereof;

FIG. 9 is a ninth image thereof;

FIG. 10 in a tenth image thereof;

FIG. 11 is an eleventh image thereof;

FIG. 12 is a twelfth image thereof;

FIG. 13 is a thirteenth image thereof; and,

FIG. 14 is a fourteenth image thereof.

The outer perimeter shown by dashed broken lines in the drawings represents a display screen or portion thereof and forms no part of the claimed design.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-14 . The process or period in which one image transitions to another image forms no part of the claimed design.

The grayscale shading in the drawing figures represents a contrast in appearance.