Having brought in the former Bologna centre half, Arteta admitted the 22-year-old will have a big part to play.
He told reporters: “I’m very happy. It took a while - it was a player that we have monitored for a year. We were really short in the backline last year in terms of numbers and we demanded so much from them.
“William Saliba, for example, played in every minute of the Premier League and we believe we had to be more protected. We identified him as a talent that can give us skill and qualities that are going to make us better. We are signing a player with a huge capacity to develop.”
On whether he will play at left-back or center half, he added: “Both positions, especially the way we want to play and the way we want to evolve in our game models. He is a player who is going to fit into what we want.”
On the club’s transfer business, he continued: “I am very happy that we’ve got Riccardo done. As I said, it was very important to have that protection in the backline because of the issues that we had, especially last year when Jurrien was injured. It increases the quality and the competition and it's very good for the team.”
On the reasons for signing another defender, he concluded: “It was the numbers. We only had six defenders in the backline and at this level you have to be really lucky to sustain the season like this. We were, because William for example and Gabriel nearly played every minute, we played more than 50 per cent more minutes than the previous season and if we are able to do that consistently over the next three or four years that’s a big question mark. Obviously you cannot just bet on that, that’s a big bet and we don’t want to take that bet.”