Display Screen or Portion Thereof with Transitional Graphical User Interface

FIG. 1 is a front view of a first image in a sequence; and,

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

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

The long-dash broken lines showing a device, the medium-dash broken line showing the display screen or portion thereof, and all other broken lines showing portions of the graphical user interface, form no part of the claimed design.