Nelson struck in the 3-0 Europa League win.
"He's made some big steps in the last month or so," Arteta told the club's website. "He's shown what he can do. Again, he's another player that wants to take you on all the time, he's very vertical, he's a great player when he runs in behind and he's very unpredictable. I really like these types of players to play in the wide positions.
"Defensively, there are things that he needs to do better and he will improve in that but he's a much more mature player. He showed a great attitude, in my opinion, to say that he didn't want to leave on loan because he believes that he's got a chance to play for this football club. He's showing that he wants to take that direction. He's performing in the right way.
"We're doing a lot of work with him. He's so willing. He's asking for more all the time. He wants individual meetings. He wants to work on the pitch in certain aspects in which we think he can improve.
"He's training really really well, he's developing as well. He had a click and we needed that click. Now it's up to him but I must say that his last performances have been really good."