(REUTERS) - 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.

The 28-year-old, 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," he told the 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.

Aubameyang 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 Milan 2-0 in the first leg at the San Siro.