London: Arsenal striker Pierre-Emerick Aubameyang said that his forced absence from the club's Europa League campaign this season was the main reason for a "frustrating" start to life at London.
Aubameyang, who joined Arsenal in January, played for former club Borussia Dortmund in the Champions League this season and UEFA's 'cup-tied' rule prevents him from representing his new team in Europe for the rest of the season.
"I am really frustrated because the rules are a bit... I don't know how to say in English but I am disappointed because I can't help my team," Aubameyang told British media.
"When I was in Dortmund, I was playing every three days but now I play once a week or have a long time between games. It is not easy... that's life. I have to deal with it."
Gabon international Aubameyang has scored three Premier League goals in five starts for the club, including in the 3-0 league win over Watford last Sunday.
"I didn't play a lot in January so it was difficult to find the rhythm. Now I'm feeling better. I work hard, I work a lot in the last weeks and I am happy because I feel better," he added.
The 28-year-old will watch from the stands as his team mates take on AC Milan in the second leg of their Europa League last 16 clash at the Emirates Stadium on Thursday. Arsenal beat AC Milan 2-0 in the first leg.
Striker Danny Welbeck, who is tasked with leading Arsenal's line in Europe in the absence of Aubameyang and the injured Alexandre Lacazette, said he was relishing the competition with his fellow forwards.
"It's competition and I embrace it," Welbeck said. "Ever since I was a kid, I've been playing for an academy with scouts all over the world that are looking for top players to come in.
"You have competition throughout your whole life and it only makes you better... gives you extra motivation."
Welbeck has struggled with hip and groin injuries this season and has not found the net since Arsenal's 4-2 FA Cup third round defeat by Nottingham Forest in January.
"My mindset's focused on looking forward, bettering myself, getting on the pitch, on the training pitch, doing what I can do to improve myself."