Display screen or portion thereof with transitional graphical user interface

[0001]FIG. 1 is a front view of a display screen or portion thereof with transitional graphical user interface showing the first image of a sequence according to our new design;

[0002]FIG. 2 is a second image thereof;

[0003]FIG. 3 is a third image thereof;

[0004]FIG. 4 is a front view of a display screen or portion thereof with transitional graphical user interface showing the first image of a sequence according to a second embodiment of our design;

[0005]FIG. 5 is a second image thereof; and,

[0006]FIG. 6 is a third image thereof.

[0007]The appearance of the transitional image sequentially transitions between the images shown in the respective embodiments of FIGS. 1-3 and FIGS. 4-6. The process or period in which one image transitions to another image forms no part of the claimed design.

[0008]The dot-dash broken line perimeter illustrates a display screen or portion thereof and forms no part of the claimed design.

[0009]The portions shown in a pattern of stipple tone illustrate areas of contrasting appearance.