Display screen or portion thereof with transitional graphical user interface

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

FIG. 2 is a front view showing a second image thereof;

FIG. 3 is a front view of a second embodiment of a display device or portion thereof with transitional graphical user interface showing a first image in a sequence, showing our new design;

FIG. 4 is a front view showing a second image thereof;

FIG. 5 is a front view of a third embodiment of a display device or portion thereof with transitional graphical user interface showing a first image in a sequence, showing our new design;

FIG. 6 is a front view showing a second image thereof;

FIG. 7 is a front view showing a third image thereof;

FIG. 8 is a front view of a fourth embodiment of a display device or portion thereof with transitional graphical user interface showing a first image in a sequence, showing our new design;

FIG. 9 is a front view showing a second image thereof;

FIG. 10 is a front view showing a third image thereof;

FIG. 11 is a front view of a fifth embodiment of a display device or portion thereof with transitional graphical user interface showing a first image in a sequence, showing our new design;

FIG. 12 is a front view showing a second image thereof; and,

FIG. 13 is a front view showing a third image thereof.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1 - 2 , 3 - 4 , 5 - 7 , 8 - 10 or FIGS. 11 - 13 .

The process or period in which one image transitions to another image forms no part of the claimed design.

The outermost pair of broken lines showing a display screen or portion thereof remaining broken lines showing elements of the graphical user interface illustrate portions of the article that form no part of the claimed design.