The experienced midfielder has been training with the Gunners for over a month after leaving Besitkas over the summer.
Oxlade-Chamberlain, formerly of Arsenal and Liverpool, has been working with the U21 squad over the past few weeks in order to keep himself fit ahead of finding a new club.
Jeorge Bird's Arsenal youth website is reporting Oxlade-Chamberlain is now training with manager Mikel Arteta's first team squad.
Now 32, Oxlade-Chamberlain was seen wearing the 'T3' shirt, which is usually reserved for trialists.
With the Gunners, Oxlade-Chamberlain made 198 appearances and scored 20 goals between 2011 and 2017.