Manchester United's team bus was attacked as it left Stamford Bridge after the 1-1 draw on Sunday night. Sir Alex Ferguson's side were heading to Euston when a bottle was hurled at the windscreen.
The windscreen was cracked but the team continued on their short trip across London without further incident and United officials were eager to play it down.
A Chelsea statement read: "It appears to be an isolated incident but we have launched a full investigation."