Display Screen or Portion Thereof with Transitional Graphical User Interface

FIG. 1 is a front view of a first image in a sequence of a display screen or portion thereof with transitional graphical user interface, according to a first embodiment; and

FIG. 2 is a front view of a second image in the sequence of the display screen or portion thereof with transitional graphical user interface, according to the first embodiment.

FIG. 3 is a front view of a first image in a sequence of a display screen or portion thereof with transitional graphical user interface, according to a second embodiment; and,

FIG. 4 is a front view of a second image in the sequence of the display screen or portion thereof with transitional graphical user interface, according to the second embodiment.

The outermost broken-line perimeter illustrates a display screen portion and forms no part of the claimed design. The remaining broken lines illustrate portions of a 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 and 3 - 4 , respectively. The process or period in which one image transitions to another image forms no part of the claimed design.