Barca announced on February 8 that Arthur had suffered a strain - a problem which it was thought would keep him out of action for a month, thus forcing him to miss the Clasico double-header, with the great rivals also tussling in LaLiga on Saturday.
But head coach Ernesto Valverde hinted in his pre-match news conference earlier on Tuesday that the Brazil international could feature in the Copa, and he has subsequently included Arthur in the travelling squad.
Jasper Cillessen is also among the party following his lay-off with a calf strain, which he too suffered at the start of the month.
Of the 'B' team players to have been involved in recent training sessions, Inaki Pena is the only one to be named in the selection.
Barca travels to the Santiago Bernabeu having been held to a 1-1 at home in the first leg.