The Irish forward turned up for the squad's flight at Glasgow Airport despite feeling sickly, but club medical staff decided he should not travel.
The last-minute development is a major blow to Hoops' manager Ronny Deila, who is already without top goalscorer John Guidetti as well as injured attacking players Kris Commons and James Forrest for Thursday's match.
Guidetti has scored nine goals in nine games since arriving on loan from Manchester City but the deal was not completed in time for him to be registered to play in Europe.
Stokes has started the last two Europa League games, including the 2-1 home win win over Astra
Former Hibs star Leigh Griffiths is another option for the Norwegian manager.
On a more positive note Craig Gordon is set to return in goal having recovered from the knee injury that kept him out of the 1-0 league win over Inverness last weekend.
Assistant manager John Collins confirmed the former Hearts and Sunderland player had joined the party flying out to Romania.
Celtic are level top with Austrian side Salzburg on three points in Group D while Astra are bottom after three straight losses.
Source : AFP
Source: AFP