Display screen or portion thereof with transitional graphical user interface

FIG. 1 is a front view of a first image of a first sequence of a display screen or portion thereof with transitional graphical user interface according to the claimed design;

FIG. 2 is a front view of a second image of the first sequence according to the claimed design;

FIG. 3 is a front view of a first image of a second sequence according to the claimed design; and,

FIG. 4 is a front view of a second image of the second sequence according to the claimed design.

The grayscale background feature of the graphical user interface is claimed subject matter.

The thick, dashed hexagons as shown in FIG. 4 portray environment and form no part of the claimed design.

The longer-length broken-line showing of a display screen and the intermediate-length broken-line showing of a display screen boundary, are included for the purpose of illustrating environmental structure and form no part of the claimed design. The remaining broken lines portray elements of the graphical user interface that are excluded from the claim.

The appearance of the transitional image transitions between the images shown in FIGS. 1-2 and FIGS. 3-4 . The process or period in which one image transitions to another forms no part of the claimed design.