Celtic keeper Artur Boruc faces up to three weeks on the sidelines should he undergo surgery on his troublesome knee.
The Poland international will miss Saturday's Clydesdale Bank Premier League clash with Kilmarnock with a thigh strain.
However, an ongoing knee problem requires an operation and he could go under the knife early next week which would rule him out of the Europa league trip to Hamburg.
Surgery may depend on the registration of back-up keeper Dom Cervi, who was not listed in the original 25-man squad submitted by the Bhoys.
The Parkhead club have asked Uefa for special dispensation to have the American involved in Germany on Thursday night, with Boruc's surgery dependant on the response.
Boss Tony Mowbray said: "Artur has a thigh injury which will take a couple of weeks to settle down.
"He also has a slight problem with his knee and he'll need something done either immediately or in a few days.
"The overriding issue is whether we can have another keeper in the squad for Hamburg.
"We are looking at the rules and we believe we can have a replacement as long as we can prove a keeper is injured.
"If we can get Artur's knee sorted now, he could hopefully be ready for the Dundee United game on November 22."