Display screen or portion thereof with transitional icon

FIG. 1 is a front view of the first image in a sequence of a display screen or portion thereof with transitional icon showing our new design;

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

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

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

FIG. 5 is an enlarged view of the first image in a sequence as shown in FIG. 1 ;

FIG. 6 is an enlarged view of the second image in a sequence as shown in FIG. 2 ;

FIG. 7 is an enlarged view of the third image in a sequence as shown in FIG. 3 ; and,

FIG. 8 is an enlarged view of the fourth image in a sequence as shown in FIG. 4 .

The broken lines in the figures depict environmental subject matter and form no part of the claimed design. The outermost broken lines in the figures represent a display screen or portion thereof and form no part of the claimed design.

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