Display Panel or Portion Thereof with a Transitional Graphical User Interface

FIG. 1 is a view of a display panel or portion thereof with a transitional graphical user interface showing a first image of a graphical user interface, illustrating our new design;

FIG. 2 is a view of a display panel or portion thereof with a transitional graphical user interface showing a second image thereof;

FIG. 3 is a view of a display panel or portion thereof with a transitional graphical user interface showing a third image thereof; and,

FIG. 4 is a view of a display panel or portion there of with a transitional graphical user interface showing a fourth image thereof.

The process, period, or order in which one image transitions to another image forms no part of the claimed design. The outermost broken lines illustrate a portion of a display panel and form no part of the claimed design. The other broken lines illustrate portions of the display screen or portion thereof with transitional graphical user interface that form no part of the claimed design.