Display Screen or Portion Thereof with Transitional Graphical User Interface

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

FIG. 2 is the second image thereof;

FIG. 3 is the first image in a sequence of a second embodiment of a display screen or portion thereof with transitional graphical user interface showing my new design; and,

FIG. 4 is the second image thereof.

The outermost broken lines showing the display screen or portion thereof are for environmental purposes only and form no part of the claimed design.

The remaining broken lines in the figures show portions of the transitional graphical user interface which form no part of the claimed design.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1 and 2 , and FIGS. 3 and 4 , respectively. The process or period in which one image transitions to another forms no part of the claimed design.