Display Screen or Portion Thereof with Transitional Graphical User Interface

FIG. 1 is a front view of the first image in a sequence of a display screen or portion thereof with transitional graphical user interface, showing our new design;

FIG. 2 is a front view of the second image thereof;

FIG. 3 is a front view of the third image thereof;

FIG. 4 is a front view of the fourth image thereof;

FIG. 5 is a front view of the fifth image thereof;

FIG. 6 is a front view of the sixth image thereof; and,

FIG. 7 is a front view of the seventh image thereof.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1 - 7 . The process or period in which one image transitions to another forms no part of the claimed design.

The broken lines showing a device, display screen and portions of the graphical user interface form no part of the claimed design.