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 of the claimed design.

FIG. 2 is a second image thereof;

FIG. 3 is a third image thereof;

FIG. 4 is a fourth image thereof;

FIG. 5 is a rear view thereof;

FIG. 6 is a side view thereof, the opposite side view being a mirror image thereof; and,

FIG. 7 is a top view thereof, the bottom view being a mirror image thereof.

The outermost evenly spaced broken lines in the drawings showing an electronic device are included for the purpose of illustrating environmental structure and form no part of the claimed design. The dot-dash broken lines show a display screen or portion thereof and form no part of the claimed design. The remaining broken lines show portions of the transitional graphical user interface and form no part of the claimed design.

The appearance of the transitional image sequentially transitions between the views shown in FIGS. 1 - 4 . The process or period in which an image transitions to another forms no part of the claimed design.