Do not Read, if you don't like spoilers.
It's either abraham or glenn.
It'll most likely be abraham, because glenn already had a false death scene.
Also note that the recent episodes abraham was getting somewhat emotional, and wanted to start a family. My money is on Abraham.
You can also see that the person was somewhat tall, and Neegan said "Taking it like a champion." Abraham is the only one who didn't look scared.
In the comics Glenn gets killed by Neegan, but a lot of the show is different from the comics. People forget that Abraham also dies by an arrow in the comics, which is how the blonde doctor died in the show.