Chelsea's defeat by Sunderland was not so surprising, even if the manner of it was, and this weekend will give a much better idea of whether the champions are in serious trouble when they travel to Birmingham.
Unlike Sunderland, who appear to be a team on the up this season, Birmingham are on a downward spiral and have sunk to third-bottom in the Premier League table. They are exactly the type of struggling team that Chelsea normally put away with ease, but there is a groundswell of opinion suggesting Chelsea might run into problems again this weekend.
The critics point to the absence of first-choice central defenders John Terry and Alex, as well as influential midfielders Frank Lampard and Michael Essien. The feeling is that Nikola Zigic, the tallest player in the Premier League, might be able to trouble Chelsea's makeshift defence in the air, even though the Serb has made little impact since moving from Spain.
That explains why Chelsea are much bigger odds than would be expected for a visit to a relegation-threatened team. In the past four seasons - only one of which was a championship-winning campaign - Chelsea have won an incredible 21 out of 24 away games against teams that finished in the bottom six.
That record suggests defeat by Birmingham, or even a draw, would be a major turn-up, because on current form it seems reasonable to expect Alex McLeish's side to finish in the bottom six. There is an interesting element to that record in that it was 100 per cent in the three seasons before Carlo Ancelotti took charge, but last season Chelsea won three, drew two and lost one in that category.
This season, however, Chelsea have won easily in their two away games against teams in the bottom six - 6-0 at Wigan and 3-1 at West Ham. In addition, they won 2-1 at 14th-placed Blackburn and only dropped points in eight games against bottom-half opposition came in the 2-0 defeat at Liverpool.