Francis Coquelin will miss Arsenal`s League Cup tie at Tottenham Hotspur on Wednesday with a knee injury but German defender Per Mertesacker, out for the last five matches, is fit to return, said manager Arsene Wenger.
French midfielder Coquelin suffered a swollen knee in Saturday`s 2-0 Premier League defeat at Chelsea where Arsenal finished with nine men after having defender Gabriel and Santi Cazorla sent off.
Gabriel and Cazorla are suspended for the first north London derby of the season at White Hart Lane as the clubs meet in the competition for the fourth time in 10 seasons.
Arsenal triumphed 5-3 on aggregate in the 2006-07 semi-finals and Spurs won 6-2 on aggregate in the 2007-08 semis.
The Gunners also won 4-1 at White Hart Lane in a third-round tie five years ago.
Just over a week ago Arsenal would have started as strong favourites following a solid start to the season while Tottenham had gone four matches without a win.
But since then Arsenal have lost to Chelsea and to Dinamo Zagreb in the Champions League while Spurs won three matches in eight days against Sunderland and Crystal Palace plus FK Qarabag in the Europa League.
With plenty at stake in what is always a fiercely contested derby, Wenger and Spurs counterpart Mauricio Pochettino are likely to field strong teams.
"I want to keep the squad together. We go game by game so I will make changes, for sure. How many? I’ve not decided yet," said Wenger.
"It will be quite an experienced squad with one or two younger players."
Pochettino said Ryan Mason, Nabil Bentaleb and Moussa Dembele had not recovered from injury.
He has not yet settled on his starting lineup or whether South Korean Son Heung-min, who has scored three times in the last two matches, will play.
"We have played three games this week and have a lot of tough games ahead," said Pochettino.
He added that he was not worried that Harry Kane, who scored 31 goals last season including both in the 2-1 league win over Arsenal in February, had not scored for Spurs yet this term.
"I am not concerned about that. I`m happy with him and the team and I am sure the goal is coming," he said.