The 20-year-old is closing in on a return to first-team action after starting for the Gunners against Fulham and could feature against Aston Villa on Monday
The 20-year-old has been sidelined since the first game of the season against Aston Villa but returned to first-team training earlier this week and managed 45 minutes at Motspur Park before being replaced by Jon Toral at half-time.
Despite only featuring in the first half the England international twice went close with shots at each end of the half and also set up Benik Afobe for a chance which the striker hit the crossbar with.
Arsenal won the game 1-0, thanks to a Thomas Eisfeld goal, to qualify for the quarter-finals of the Premier League Cup where they will face Chelsea.
Prior to being named in the Under-21 team, Arsene Wenger revealed Oxlade-Chamberlain would be fit to face Aston Villa on Monday.
"It is unbelievable because he played the first game of the season, against Aston Villa, and now he is back and available and it is against Aston Villa again," said the Arsenal manager.
"That makes it five months where has been completely out, so that means he is fresh and that should give us a boost."
Carl Jenkinson also insists the return of the winger following Theo Walcott's season-ending knee injury is a welcome boost to the club.
“He's a really good friend of mine but football-wise, he's a fantastic player who brings an awful lot to the team," Jenkinson told the club's official website.
"To have him back in and around the group is a boost for everyone - he's only young but he's a key member of the squad.”