Olivier Giroud has raised his game to another level after Theo Walcott took his place in the Arsenal team earlier in the season, according to Mathieu Flamini.

Walcott was Arsène Wenger’s preferred central striker until he injured a calf in the Capital One Cup loss at Sheffield Wednesday in October. Giroud has been back in since then and he was the hat-trick hero of the club’s 3-0 win at Olympiakos on Wednesday night which carried them into the Champions League last 16.

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“Competition is very important in the big teams – it makes players stronger and that is what happened,” the midfielder Flamini said. “It is tough competition up front and Olivier is responding very well because he is playing better and better. That is part of the game and if you want to play at a big club you have that competition.”

Giroud’s goals against Olympiakos took his tally to 11 in 14 appearances and his was a performance marked by bravery. He took a few digs from his markers and rolled an ankle in the second half, which needed lengthy treatment. But he dusted himself down to score his second goal moments later.

The criticism of Giroud has been that he is not the world-class striker Arsenal need to win the Premier League. Thierry Henry has endorsed this view although he has attempted to backtrack from it.

Giroud can have badly off-colour days – he endured a personal nightmare in the Champions League last-16, first leg home loss to Monaco last season – and they have not helped his cause. But he has scored goals at a consistent rate, finishing with 17, 22 and 19 in his first three seasons at the club. With 13 in all competitions so far this time, he is on course for a personal best.

“All great strikers have to respond in the big games,” Flamini said. “Olympiakos was a good test for us and Olivier responded well. It was a great performance from him and he helped the team very much. He is a top scorer.

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“He deserves the credit and I think he gets it. I have not seen it anywhere or from anyone that he is not a top goalscorer. He is proving it on the pitch so is doing very well. I am glad and happy for him.”

Arsenal face Aston Villa on Sunday and attention will then turn to Monday’s draw for the Champions League last 16 when they will be paired with either Barcelona, Real Madrid, Atlético Madrid, Wolfsburg or Zenit St Petersburg.

“We obviously don’t want Barcelona as they are a top team,” Flamini said. “But for the rest, we will see. We played Monaco last year and we thought it would be a bit easier maybe, and it was not the case, so whoever we play we will give 100%.

“We showed great spirit against Olympiakos and I think it was the perfect performance as we did not concede any goals. We had a good balance. We had the chance to prove to everyone that we have the qualities of being a top team in the Champions League. We did it playing some good football.”