Display screen or portion thereof with transitional graphical user interface

FIG. 1 is a front view of a first image in a sequence for a display screen or portion thereof with transitional graphical user interface according to a first embodiment; and

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

FIG. 3 is a front view of a third image in the sequence thereof; and

FIG. 4 is a front view of a fourth image in the sequence thereof.

FIG. 5 is a front view of a first image in a sequence for a display screen or portion thereof with transitional graphical user interface according to a second embodiment; and

FIG. 6 is a front view of a second image in the sequence thereof;

FIG. 7 is a front view of a third image in the sequence thereof; and,

FIG. 8 is a front view of a fourth image in the sequence thereof.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-4 and FIGS. 5-8 . The process or period in which one image transitions to another image forms no part of the claimed design.

The outermost broken line rounded rectangle showing an electronic device illustrates environmental subject matter. The broken line showing a display screen, and all other broken lines showing portions of the graphical user interface illustrate portions of the article. None of the aforementioned broken line subject matter forms part of the claimed design.