Use your meele. I had trouble with it too until I experimented with fighting styles. You need to close the gap quickly, I used the forward launch thing, then meele him which almost completely breaks his shield, then you have 5 seconds or so to get as much damage on him until his shields come back. Rinse and repeat. Keep distance and hide while your abilities reload and keep an eye on your energy, if it depletes, you’re screwed. Also don’t forget you have three med packs.