Arsène Wenger is adamant that Olivier Giroud has not been affected by recent problems in his private life and that the striker is in the right frame of mind to return for Arsenal against Sunderland. However, the Arsenal manager has decided to take Mesut Özil, who was criticised for his performance in Wednesday's 2-0 defeat by Bayern Munich after having an early penalty saved, out of the firing line and omit him from the squad.

There has been speculation over Giroud following a story in the Sun newspaper that he had sneaked a woman into the team hotel on the night before the Crystal Palace game on 2 February, and the Frenchman was named as a substitute in Arsenal's last two matches. With Giroud's marriage crisis dominating headlines, the inexperienced Yaya Sanogo was surprisingly preferred up front in Sunday's FA Cup win over Liverpool and then in the first leg of the last-16 Champions League tie against Bayern.

But Wenger has maintained all along that Giroud was omitted for footballing reasons, citing a string of tired performances, rather than for breaking club rules. He confirmed that Sanogo will return to the bench against Sunderland and insisted that it will not be a problem for Giroud to start.

"I am not worried for Giroud," Wenger said. "His head is in the right place. He will be focused. He's a great player. He is a great fighter as well. He has been successful until now; during this season he's played a big part in it. The same people who asked me why didn't he play are now asking me now why I rested Giroud. It's part of the job to decide who plays, it's debatable every time. I have to live with that and I have to make my decisions with my conscience and I just make my decision based on who can help us win the next game."

Giroud, Arsenal's leading scorer with 14 goals, had not registered for three games before being dropped, which Wenger put down to fatigue. "Recently he's been a bit less fresh and it's shown a little bit in his game," he said. "Mentally he's always focused. He always wants to play. I just felt physically he was a bit less sharp.

"He is a strong man. We all have our weaknesses and strengths. Some of us when we have problems outside the field use the pitch or the work to forget about our problems. Some of us are different but he is one of them who will focus completely on the pitch."

While Giroud prepares to return against Gus Poyet's side, the situation was less clear regarding Özil. Wenger admitted on Wednesday that the German failed to overcome the disappointment of missing from the spot in the seventh minute against Bayern – his feeble effort was easily saved by Manuel Neuer – and at £42.5m the club's record signing has been underwhelming recently. Wenger said that Özil was still hurting.

"I think what's important is always the team and you never want to hurt any player but you don't want to give him any favour," he said. "You have to pick the team who can win the next game. It's our job and the players' job to adapt to that and not to think too much about individual cases. What is important is the team and to win the next game.

"You have to rotate until the end of the season when you look at the challenges we have in front of us, it's vital. We have played at Liverpool, against Manchester United, against Liverpool, against Bayern Munich. They are only human beings."

However, Wenger stressed that a missed penalty is not the end of the world. He pointed out that Bayern also missed theirs and that a statue of Dennis Bergkamp is being unveiled outside the Emirates Stadium on Saturday morning, even though the Dutchman had a crucial penalty saved in the last minute of Arsenal's FA Cup semi-final defeat against Manchester United in 1999.

Wenger plans to discipline Wojciech Szczesny for the obscene gesture the goalkeeper made as he left the pitch after being sent off against Bayern, although he is unlikely to face a further charge from Uefa. "We'll deal with that," Wenger said. "We don't agree with that. It was frustration but we are professionals, me included, and we have always to master reactions. Wojciech is part of that as well."