Display screen or portion thereof with transitional graphical user interface

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

FIG. 2 is the second image thereof;

FIG. 3 is the third image thereof;

FIG. 4 is the fourth image thereof;

FIG. 5 is the fifth image thereof;

FIG. 6 is the sixth image thereof;

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

FIG. 8 is the second image thereof;

FIG. 9 is the third image thereof;

FIG. 10 is the fourth image thereof;

FIG. 11 is the fifth image thereof;

FIG. 12 is the sixth image thereof.

FIG. 13 is the seventh image thereof;

FIG. 14 is the eighth image thereof;

FIG. 15 is the ninth image thereof; and,

FIG. 16 is the tenth image thereof.

The broken lines in the figures depict portions of the graphical user interface that form no part of the claimed design. The outermost broken line showing of a display screen or portion thereof forms no part of the claimed design.

The appearance of the graphical user interface sequentially transitions between the images shown in FIGS. 1 through 6 and FIGS. 7 through 16 . The process or period in which one image transitions to another forms no part of the claimed design.