The Blues are now set to travel to Croatia to face Dinamo Zagreb on Tuesday, September 6 - only two days after welcoming the Hammers to Stamford Bridge.
Next weekend’s game has therefore been brought forward from Sunday, September 4 at 2pm BST to Saturday, September 3 with a kick-off time still to be confirmed.
The short-notice move comes despite a notice period of three weeks typically targeted for broadcast changes.
Although this alteration at just one week’s notice is not broadcast-related, the fixture was earlier this month announced as a Sky Sports match despite a 50 per-cent chance that Chelsea would be drawn to play on the following Tuesday in Europe.
Next Saturday promises to be a busy day in the Premier League with the Merseyside derby set for the lunchtime kick-off and Aston Villa facing Manchester City in the 5.30pm game.
Therefore either a 3pm or 7.45pm start time is likely to be confirmed for Chelsea versus West Ham.