Bremen's Boenisch undergoes knee surgery

BERLIN, Sept 21 (Reuters) - Werder Bremen defender Sebastian Boenisch underwent knee surgery and will be out for a yet undetermined period of time, the Bundesliga club said on Tuesday as their defensive injuries continued to pile up.

Bremen, who came from two goals down to draw 2-2 with Tottenham Hotspur in their Champions League Group A opener last week, are already without injured central defenders Naldo and Per Mertesacker.

They will all miss Tuesday's league match against Hanover 96 as will striker Claudio Pizarro, who is recovering from a muscle injury.

Defender Dominik Schmidt has come into the squad as a possible replacement for Boenisch, with the 23-year-old still waiting for his first Bundesliga appearance this season.

Boenisch had an operation on Monday after nagging knee problems. He will undergo further checks on Tuesday to determine the length of his absence, Werder said.

Werder are languishing in 11th place after a rocky start to the season saw them pick up only four points from four matches.