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 of the new design;

FIG. 2 is a second image thereof;

FIG. 3 is a third image thereof;

FIG. 4 is a fourth image thereof; and,

FIG. 5 is a fifth image thereof.

The dot-dash broken lines in the drawings show a display screen or portion thereof and form no part of the claimed design. The remaining broken lines in the drawings, including the evenly spaced broken lines showing an electronic device and portions of a graphical user interface, and the lined-through text, graphics, and other elements of the graphical user interface, form no part of the claimed design. The faded portions within broken lines, including the faded portions between the broken line around the outside of the icon and the broken line around the surrounding rectangle, and the faded portions inside the broken-line areas defined within the icon, form no part of the claimed design.

The appearance of the transitional images sequentially transitions between the views of FIGS. 1 - 5 . The process or period in which an image transitions to another forms no part of the claimed design.