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 the first image in a sequence.

FIG. 2 is the second image of the sequence.

FIG. 3 is the third image of the sequence.

FIG. 4 is the fourth image of the sequence.

FIG. 5 is the fifth image of the sequence; and,

FIG. 6 is the sixth image of the sequence.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1 - 6 . The process or period in which one image transitions to another image forms no part of the claimed design.

The outermost broken line rectangle in each figure illustrates a display screen or portion thereof and forms no part of the claimed design.