The virus hit Antonio Conte’s squad in the days leading up to Sunday’s 2-0 defeat at Manchester United, and went some way to explaining their off colour performance at Old Trafford.
Spain full-back Marco Alonso, despite being named in the line up on Sunday, complained of feeling ill after the pre-match warm-up.
Antonio Conte's squad has been struck down by a virus
Gary Cahill is the latest Chelsea star to be hit by the bug
Chelsea’s medical staff assessed him and the wing-back was withdrawn from the team, with the leaders then losing to leave their advantage at the top off the Premier league trimmed to four points from Tottenham with six games still to play.
But several other players were also affected by the virus, which had set in towards the end of last week.
Chelsea and Tottenham fans react to Antonio Conte's mind games Mon, April 17, 2017
Chelsea manager Antonio Conte has provoked Tottenham Hotspur fans with perceived mind games after Spurs cut the Blues' lead at the top of the Premier League to just four points
Play slideshow Getty Images 1 of 13
Chelsea and Tottenham Hotspur fans react to Antonio Conte's perceived mind games
One theory is that the bug spread through the squad at a team bonding meal – one of several arranged by Conte over the season to strengthen the group – last Thursday.
Now centre back and captain Cahill has gone down with the bug – but he is expected to recover in time for Saturday’s FA Cup semi-final clash with Spurs at Wembley.
Get Quotes on Home Insurance