LONDON • Chelsea's uncharacteristically off-colour performance at Manchester United on Sunday has been put down partly to a bug that affected members of Antonio Conte's squad and ruled Marcos Alonso out of the Premier League game.
Alonso was still suffering the effects of the virus on Saturday night and, despite being named in the starting line-up at United, complained of feeling ill after the pre-match warm-up.
The Blues' medical staff assessed him and the wing-back was withdrawn from the team, with the league leaders going on to lose the match 2-0 to leave their advantage at the top trimmed to four points from Tottenham Hotspur with six games left to play.
Alonso's late withdrawal forced Cesar Azpilicueta to fill in on the left, with Kurt Zouma drafted in as a right-sided full-back and it clearly affected the balance of Conte's team.
Yet, Alonso was not the only Chelsea player still suffering from the virus which had set in within the squad towards the end of last week.
One theory that has been considered by the club is that the bug had spread through the squad at a team bonding meal - one of a number arranged by Conte over the course of the season to strengthen the group - last Thursday evening.
Victor Moses, only just returned from a calf injury, had also been hampered. The midfielder started the game but had to be withdrawn nine minutes into the second half, prompting further disruption to the visitors' approach.
Diego Costa is understood to have been unwell and, like Moses and Alonso, missed training at the end of last week before the trip to Old Trafford.
The striker declared himself fit but struggled to make much of an impact during the game.
The hope at Chelsea is the trio will be fit to play in the FA Cup semi-final against Tottenham on Saturday, when they hope to inflict psychological damage on their nearest rivals in the title race.
Yet, the effects of the bug were still being felt at Cobham on Tuesday when defender Gary Cahill reported unwell.
Goalkeeper Thibaut Courtois, who hurt his ankle while playing basketball at a Chelsea promotional shoot for the National Basketball Association (NBA) last week, is hoping to prove his fitness for the Wembley tie.