Display Screen or Portion Thereof with Transitional Graphical User Interface

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

FIG. 2 is a second image thereof;

FIG. 3 is a third image thereof;

FIG. 4 is a fourth image thereof; and,

FIG. 5 is a fifth image thereof.

The appearance of the figures sequentially transitions between FIGS. 1 through 5 . The process or period in which one image transitions to another forms no part of the claimed design.

The outer perimeter broken lines in the drawings represent a display screen or portion thereof and form no part of the claimed design. The remaining broken lines in the drawings illustrate portions of the graphical user interface that form no part of the claimed design.