First, Tello is an exciting winger who can play up front if need be. Second, the dude's quick, and with Arsenal now left without Theo Walcott's speed on the wing for the rest of the season, they're in need of someone who can be a recipient of Mesut Ozil's well-placed through balls. Lastly, Tello's being blocked at Barcelona at the moment by other trusted players, and much like Gerard Deulofeu's loan to Everton, Barcelona can ensure the growth of their talented young players with match time in highly-competitive clubs and competitions.
Our friends over at Barca Blaugranes have seemingly played down the prospects of such a move, however Marca continues to fan the flames of this rumor by suggesting there's a bit more to it than people think at the moment. Tello has twenty appearances in all competitions this season, but only six as a starter and, out of those six starts, four came in the Copa del Ray cup competition. By moving to Arsenal, one would imagine he'd get far more starts and meaningful playing time than staying at Barcelona. Whether or not this happens, though, is a completely and entirely different story.
We'll keep track of where this bit of news heads as the day progresses. Until then, feel free to pun away in the comments.