Torreira is ostensibly fine according to match commentary. The way he fell, I thought it may be a stomach muscle pull or possibly a cracked rib, but not serious.
Reasonable performance to get the job done after a languid start: nice goal from Sokratis and fortunate one from Nketiah, but Martinez wasn't overly troubled and Portsmouth never looked likely to fight back. Nelson looked sharp after a prolonged absence.
Re: Maitland-Niles, I am not surprised Arteta has iced him. He isn't good enough in any position, a level or three below most of the younger crop. A direct comparison is Saka: equally out of position at fullback but plays a progressive game, has good interplay and a lot of production, and hasn't been found wanting defensively. Then you have Maitland-Niles: careless in possession, inconsistent in attacking areas, and defensively weak. I don't care for players who just run around a lot, but AMN never seems like he is really expending for the team, he's far too relaxed.