The Republic of Ireland international needed oxygen as he was carried off on a stretcher having made a fine save from Abou Diaby midway through the second-half of Saturday's game at Emirates Stadium.
His departure from the field prompted an unexpected debut for Faroe Islands goalkeeper Gunnar Nielsen, who could now face Aston Villa, Tottenham and West Ham with regular number two Stuart Taylor recovering from knee surgery.
Ideally City boss Roberto Mancini would like to recall Joe Hart from his loan spell with Birmingham as City look to secure fourth spot in the Premier League, but it's believed no such clause exists in the season long agreement.
Mancini told the club's official website: "Shay's injury will be a problem. It's not good for us because Shay is a fantastic goalkeeper. He is important to us, but in football you can always get injured.
"Shay is in hospital, but we have 10 days and must play three big games. Gunnar came on and did very well. Stuart is still some way off and everyone must be 200% now."