Display screen or portion thereof with transitional icon

FIG. 1 is a front view of a display screen or portion thereof with transitional icon 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 showing a third image thereof;

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

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

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

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

FIG. 8 is a front view showing an eighth image thereof;

FIG. 9 is a front view showing a ninth image thereof; and,

FIG. 10 is a front view showing a tenth image thereof.

The outermost perimeter illustrated by a pair of dashed broken lines depicts a display screen or a portion thereof and forms no part of the claimed design.

The appearance of the transitional icon sequentially transitions between the images shown in FIGS. 1-10 . The process or period in which one image transitions to another image forms no part of the claimed design.