Blackwell said: "If the first prognosis is correct he will need an operation which would keep him out for up to three months. The thumb isn't broken but he has severed the ligament and has split the capsule around the thumb.
"In some respects it would be better if he had simply broken it. As a result we are seeking a second opinion to see if there is a route to take without the operation."
First-choice goalkeeper Paddy Kenny is sidelined until April as he serves a nine-month drugs ban and Malta international Justin Haber is on loan at sister club Ferencvaros in Hungary, which leaves Mark Bunn, on loan from Blackburn, as the only senior goalkeeper.