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 showing a first image of a first embodiment of the claimed design;

FIG. 2 is a front view showing a second image of the first embodiment;

FIG. 3 is a front view of a first image of a second embodiment of the claimed design;

FIG. 4 is a front view showing a second image of the second embodiment;

FIG. 5 is a front view of a first image of a third embodiment of the claimed design;

FIG. 6 is a front view showing a second image of the third embodiment;

FIG. 7 is a front view of a first image of a fourth embodiment of the claimed design; and,

FIG. 8 is a front view showing a second image of the fourth embodiment.

The appearance of the transition is sequential from FIG. 1 to FIG. 2 in the first embodiment, from FIG. 3 to FIG. 4 in the second embodiment, from FIG. 5 to FIG. 6 in the third embodiment, and from FIG. 7 to FIG. 8 in the fourth embodiment. The process or period in which an image transitions to another image forms no part of the claimed design.

The longer-length broken-line showing of a portion of a display screen and the intermediate-length broken-line showing of a display screen boundary, are included for the purpose of illustrating environmental structure and form no part of the claimed design. The remaining broken lines show elements of the graphical user interface that form no part of the claimed design.