Arsenal boss Unai Emery has told Mesut Ozil he faces a fight to regain his place in the team after being left out of Friday's (AEST) Europa League win over Standard Liege.

Ozil was not in the squad as the Gunners cruised to a 4-0 win at Emirates Stadium, with Gabriel Martinelli scoring twice before further goals from Joe Willock and Dani Ceballos.

The 30-year-old has only played twice this season, in the 2-2 Premier League draw at Watford and last week's 5-0 EFL Cup defeat of Nottingham Forest, in which he was captain.

Emery has told the playmaker to work hard to win back a spot for Sunday's league game at home to Bournemouth.

When asked why Ozil was not involved against Standard, he told a news conference: "I am thinking every time to decide the best players for each match, and the best players in the squad to play and to help us. If I decided he is not in the squad, it's because I think another player deserved it more."

Pressed on what Ozil must do to regain his place, Emery replied: "Continue working. Tomorrow [Friday], we have training, and Sunday we have another match and we are going to decide the same: the best team possible to achieve our target, which is to win on Sunday and adapt to the difficulty of Bournemouth."

Emery was delighted with the performance of Martinelli, who also scored twice in the win over Forest, although he does not believe the teenager's best position is as a central striker.

"He played in pre-season with us and in every training session he showed he is hungry to be with us," said Emery.

"His pace is amazing and, in pre-season, he played in different positions. He preferred to play left wing but he played as a right-winger as well. He played as a striker in Brazil; it's not the best position for him.

"The first thing in his mind is to help us. His performance tonight and his attitude was amazing. In pre-season he was perfect with us all the time in training, playing, and I spoke with him to be calm because if he continues with training and with this hunger, he is going to do well.

"Our targets for the season are very important to achieve, but each match for the young players, when they have chances to play, if they play like some did tonight then they deserve to be with us. Matches like tonight I think are good because it is an important competition after the Premier League and they are deserving of being in the next matches with us."

Emery was also pleased with the performance of Kieran Tierney, who set up Martinelli for the opening goal.

"After his injury, he's coming back with a good attitude, he played last week against Nottingham Forest for 80 minutes," he said of the left-back.

"It was a good performance and tonight was a good performance. We are a better, competitive team with him and Sead Kolasinac at left-back. We are very happy with him."