Display screen or portion thereof for a transitional graphical user interface

FIG. 1 is a front view of a first image in a sequence for a transitional generated image for a display screen or portion thereof, showing my new design, in which a mobile terminal is provided in broken lines to illustrate an example environment;

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

FIG. 3 is a front view of a third image thereof;

FIG. 4 is a front view of a fourth image thereof;

FIG. 5 is a front view of a fifth image thereof;

FIG. 6 is a front view of a sixth image thereof;

FIG. 7 is a front view of a seventh image thereof;

FIG. 8 is a eighth image thereof; and,

FIG. 9 is a front view of FIG. 1 which illustrates an example environment.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1 through 8 . This process or period forms no part of the claimed design. The long and short dashed broken line showing of a mobile terminal in FIGS. 1-8 forms no part of the claimed design. The mobile terminal, display screen, and the text, numbers, symbols and images of the graphical user interface shown in broken line in FIGS. 1-9 depict subject matter that forms no part of the claimed design.