Computer Display Screen or Portion Thereof with Transitional Graphical User Interface

FIG. 1 is a front view of a first image in a sequence of our design for a computer display screen or portion thereof with transitional graphical user interface; and,

FIG. 2 is a front view of the second image in the sequence thereof.

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

The outermost broken line rounded rectangle showing an electronic device illustrates environmental subject matter. The broken line showing a display screen, and all other broken lines showing portions of the graphical user interface illustrate portions of the article. None of the aforementioned broken line subject matter forms part of the claimed design. Thus, the area between the broken line showing the display screen, excluding all other broken lines, form the claimed design.