Display Screen or Portion Thereof with Transitional Graphical User Interface

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

FIG. 2 is the second image thereof;

FIG. 3 is the third image thereof;

FIG. 4 is the fourth image thereof;

FIG. 5 is the fifth image thereof;

FIG. 6 is the fourth image thereof; and,

FIG. 7 is the fifth image thereof.

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

The boundary lines shown in dot-dash form indicate the bounds of the claimed design. It is understood that the claimed design extends to the boundary line but does not include the boundary line.

The outermost, evenly-dashed broken lines in the figures indicate a display screen or portion thereof, which forms no part of the claimed design.