Pasanen doubtful as Werder problems deepen
Werder, who must win in London to have any chance of advancing, are already without nine players, including captain Torsten Frings and strikers Claudio Pizarro and Marko Arnautovic.
Finland international Pasanen could still travel to London on Wednesday morning if he was fit enough, officials said.
Coach Thomas Schaaf has included several players from the under-23 team to make up the numbers in the squad.
"There is hardly anyone who thinks we can pull this off and maybe that is the challenge we need," said Schaaf, whose team have conceded 13 goals in their last four league games.
Werder are last in Group A with just two points from four games. They need to win both their remaining fixtures to have any chance of progressing.