Display Screen or Portion Thereof with Transitional Graphical User Interface

FIG. 1 is a first image of a first embodiment 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;

FIG. 5 is a first image of a second embodiment in a sequence for a display screen or portion thereof with transitional graphical user interface showing my new design;

FIG. 6 is a second image thereof;

FIG. 7 is a third image thereof; and,

FIG. 8 is a fourth image thereof.

The even-length broken lines illustrate portions of a display screen and form no part of the claimed design.

The appearance of the figures sequentially transitions between FIGS. 1 through 4 , and between FIGS. 5 through 8 . The process or period in which one image transitions to another forms no part of the claimed design.