Novak Djokovic beat Tomas Berdych in straight sets this afternoon, opening up a clear path for Andy Murray to advance to the semi-final stage.
The British number one takes on Jo-Wilfried Tsonga this evening, and the earlier result in Group A means Murray can afford to lose the match, as long as he wins one set in the process.
If Murray loses in straight sets, he is out of the tournament at the O2 Arena.
Djokovic's result means it is impossible for Murray to top Group A, even if he beats Tsonga in straight sets.
Finishing second in Group A is likely to mean a meeting with Roger Federer, who plays tomorrow, in the final four.