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 in a sequence, showing our new design;

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

FIG. 3 is a front view showing a third image thereof;

FIG. 4 is an enlarged view of the claimed portion in FIG. 1 ;

FIG. 5 is an enlarged view of the claimed portion in FIG. 2 ; and,

FIG. 6 is an enlarged view of the claimed portion in FIG. 3 .

The outermost perimeter illustrated by a pair of dashed broken lines represents display screens or portions thereof and forms no part of the claimed design. The remaining dashed broken lines illustrating portions of the graphical user interface form no part of the claimed design. The dotted broken lines in FIGS. 1 and 4 are a part of the claimed design. The contrast shown in grayscale in the figures represents a contrast of appearance.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-3 . The process or period in which one image transitions to another image forms no part of the claimed design.