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 a front view showing a fourth image thereof;

FIG. 5 is a front view showing a fifth image thereof; and,

FIG. 6 is a front view showing a sixth image thereof.

The outer perimeter shown in broken lines in the drawings represents a display screen or portion thereof and forms no part of the claimed design.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1 - 6 . The process or period in which one image transitions to another image forms no part of the claimed design.

The contrast shown in grayscale in the figures represents a contrast of appearance.