If his start position at 0 frames matches his end position at, say, 300 frames, you render from 0 to 299, re-import that into AE, and under file>interpret>main, set it to loop for as long as you want. A seamless loop is always one frame less – otherwise you’ll see the identical frame twice, at the end then the restart of the sequence while looping.
Now if those two positions don’t match, you’re probably out of luck. If they are very very closely offset, you might be able to morph to hide the offset using Re:Flex. If they’re not that close, you should have just shot the person walking in circles over and over again for much longer than the time needed. Hey, tape is cheap, post isn’t.