Display screen or portion thereof with transitional graphical user interface

FIG. 1 is the first image in a sequence for 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; and,

FIG. 6 is an enlarged view of the portion 6 encircled in FIG. 5 .

The outer perimeter shown in evenly-spaced dashed broken line in the figures depicts a display screen or portion thereof and forms no part of the claimed design. The remaining evenly-spaced dashed broken lines in the figures depict portions of the transitional graphical user interface that form no part of the claimed design. The dot-dot-dash broken lines in FIGS. 5 and 6 encircle portions of the claimed design that are shown enlarged in FIG. 6 , and form no part of the claimed design.

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