Display screen or portion thereof with transitional graphical user interface

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

FIG. 2 is the second image thereof;

FIG. 3 is the first image in a sequence of a display screen or portion thereof with transitional graphical user interface showing our new design according to a second embodiment;

FIG. 4 is the second image thereof;

FIG. 5 is the first image in a sequence of a display screen or portion thereof with transitional graphical user interface showing our new design according to a third embodiment;

FIG. 6 is the second image thereof;

FIG. 7 is the first image in a sequence of a display screen or portion thereof with transitional graphical user interface showing our new design according to a fourth embodiment; and,

FIG. 8 is the second image thereof.

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

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1 - 2 , 3 - 4 , 5 - 6 , and 7 - 8 , respectively. The process or period in which one image transitions into another image forms no part of the claimed design.