The company releases its quarterly results on Thursday.
Sources at GM say the job losses could range from 6,000 to nearer 12,000.
GM Europe, which currently employs 63,000 staff, had no comment. It said last week it would present the plan by the end of November in time for it to have an impact on 2005 results.
Carl-Peter Forster, president of GM's European operations, told Reuters last month he wanted to see a "massive reduction in the wage bill" and that GM thought a 30% cut in its European labour costs was a reasonable target by the end of the decade.
GM posted its last annual profit in Europe in 1999 and its operations in the region have been under an almost constant state of restructuring for years.
GM and its unions are at a standoff over GM's plans to freeze pay at German plants until 2009 and get other concessions it says it needs to become more competitive.
The Financial Times’ German paper on Monday cited an unidentified GM executive as saying the group aims to cut its costs in Europe by more than £340m in a drive a return to profitability.
A spokesman for the IG Metall metalworkers union said such reports seemed to be unhelpful attempts by GM management to scare workers into making concessions.