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 an enlarged view of the solid-line and broken-line square feature in the lower right corner of FIG. 1 , shown separately for clarity of illustration;

FIG. 4 is an enlarged view of the solid-line and broken-line square feature in the lower right corner of FIG. 2 , shown separately for clarity of illustration;

FIG. 5 is another front view of FIG. 1 , but shown without the relatively longer broken lines inside the display screen for clarity of illustration; and,

FIG. 6 is another front view of FIG. 2 , but shown without the relatively longer broken lines inside the display screen for clarity of illustration.

The relatively shorter broken lines in the solid- and broken-line square feature shown in the lower right corner of FIGS. 1, 2, 5, and 6 , and isolated in FIGS. 3 and 4 , form part of the claimed design. The outermost perimeter depicted in relatively longer broken lines illustrates the display screen or portion thereof and forms no part of the claimed design. The remaining broken lines illustrate portions of the graphical user interface and form no part of the claimed design.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-2 . The process or period in which one image transitions to another image forms no part of the claimed design.