Chelsea and Thomas Tuchel were handed a massive injury blow during the shock 5-2 defeat to Premier League strugglers West Brom at Saturday lunchtime.
Christian Pulisic, who gave the Blues the lead when he was first to react to Marcos Alonso's free-kick hitting the post, did not play any part of the second half at Stamford Bridge as he was substituted for Mason Mount.
The reason for his withdrawal was spotted by some eagle-eyed Chelsea supporters.
Ahead of the second half, footage on social media - shown by NBCSN - showed Pulisic pulling up and hobbling over to the bench after attempting to sprint between cones to regain sharpness.
It was at that moment where he told his Tuchel he had sustained an injury, or at least that he felt a tweak in one of his muscles and the decision to take him off was made immediately.
"Christian did a sprint when he came back out for the second half and said that he felt his hamstring would not survive the game if he continued," Tuchel said after the game.
"So we had to make the decision to substitute him straight away."
However, upon closer inspection of the aforementioned video, it was clear that Tuchel was not best pleased when Pulisic was complaining about his hamstring.
At the time Pulisic went off, the Blues were trailing 2-1 after the Baggies took full advantage of the hosts being reduced to 10-men following Thiago Silva's red card.
And without the USA international, Tuchel's side would go on to lose 5-2 in a result that has blown the race for a top-four finish wide open.
Pulisic has had rotten luck with injuries so far this season, already missing 14 games across all competitions through four separate problems.
And he could be set for another spell on the sidelines.
Chelsea are in Champions League action on Wednesday as they face Porto in a quarter-final first-leg before making the short trip to Selhurst Park for a London derby with Crystal Palace next weekend.
