Arthur accepts he made a mistake by attending Neymar's birthday shortly before Barcelona's Copa del Rey clash with Real Madrid.
The Brazil midfielder, Neymar's international team-mate, celebrated with the former Barca star in Paris at the start of February.
Arthur started against Madrid in the first leg of the Copa Clasico semi-final two days later but suffered a hamstring injury during the game.
LIVE | Ernesto Valverde & Arthur’s press conference#BarçaOL https://t.co/Svw4giEXCO— FC Barcelona (@FCBarcelona) March 12, 2019
Speaking to reporters ahead of Wednesday's Champions League clash with Lyon, Arthur made clear his regret at going to the event.
"I think so," Arthur told a news conference when asked if he made an error. "Sometimes life has these ups and downs, I wanted to go but I'm also aware of my responsibilities.
"I knew what I was doing but if anybody was upset by that, it's a process my team-mates have helped me with a lot. I'm very grateful to the club management, who have always shown a lot of concern about me.
"It was a difficult time, but the joy came back as I've recovered from my injury. I know I have to improve a lot as a person, when I've needed help I've always received that help and I'm very happy to be here at Barca."
Neymar, who missed Paris Saint-Germain's Champions League shock exit to Manchester United due to injury, has been linked with a return to Barcelona.
But Real Madrid are also reportedly interested in the forward, with Arthur accepting Neymar could yet join Barca's rivals.
"It's an option for him that he could think about," Arthur said. "He'd need to speak to his family about it.
"As a friend I just wish him the very best. I don't know what he'll choose to do.
"Me, as a friend, all I can do is wish him the very best in the world. It's not me who signs the papers."
Barca's 0-0 draw at Lyon in the first leg gives them the advantage ahead of the return fixture at Camp Nou, but Arthur noted surprise results elsewhere in the competition will keep the LaLiga leaders on their toes.
"Madrid and PSG are big teams and they haven't qualified, the teams that beat them have played better, they deserved the win," Arthur added.
"We have to resepct the teams that are in the competition. We're focused on this game, totally focused on this game. We're expecting a lot from Lyon, we know it's going to be very hard to win."