Display screen or portion thereof with transitional graphical user interface

FIG. 1 is a front view of a display screen or portion thereof with transitional graphical user interface of a first image;

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

FIG. 3 is a front view of a third image thereof; and,

FIG. 4 is a front view of a fourth image thereof.

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

The area between the display screen boundary and the outermost edge of the graphical user interface depicts portions of the article that forms no part of the claimed design.

The outermost broken line rectangle shows the display screen and forms no part of the claimed design. All other broken lines show portions of the graphical user interface and form no part of the claimed design.