Display Screen or Portion Thereof with Transitional Graphical User Interface

FIG. 1 is a front view of the first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design according to a first embodiment; FIG. 2 is the second image thereof; FIG. 3 is the third image thereof; FIG. 4 is a front view of the first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design according to a second embodiment; FIG. 5 is the second image thereof; FIG. 6 is the third image thereof; FIG. 7 shows a portion of FIG. 1 , depicting only the claimed subject matter of FIG. 1 , shown separately for clarity of illustration; FIG. 8 shows a portion of FIG. 2 , depicting only the claimed subject matter of FIG. 2 , shown separately for clarity of illustration; FIG. 9 shows a portion of FIG. 3 , depicting only the claimed subject matter of FIG. 3 , shown separately for clarity of illustration; FIG. 10 shows a portion of FIG. 4 , depicting only the claimed subject matter of FIG. 4 , shown separately for clarity of illustration; FIG. 11 shows a portion of FIG. 5 , depicting only the claimed subject matter of FIG. 5 , shown separately for clarity of illustration; and, FIG. 12 shows a portion of FIG. 6 , depicting only the claimed subject matter of FIG. 6 , shown separately for clarity of illustration. The outer perimeter shown in broken lines in the figures illustrates a display screen or portion thereof and forms no part of the claimed design. The broken lines showing of the two larger circles and the plus signs in lighter gray tones in FIGS. 1 , 4 , 7 , and 10 and the broken lines showing of the larger circle and the plus signs in lighter gray tones in FIGS. 2 , 5 , 8 , and 11 form part of the claimed design. The remaining broken lines in the figures illustrate portions of the graphical user interface that form no part of the claimed design. The gray shading in the drawings indicates a contrast of appearance.