The Blues boss said he did not yet know the severity of the issue but added that it was a “disappointment” going into the busy festive period.
Ziyech was forced off less than half-an-hour into the clash at Stamford Bridge and had to be replaced by Christian Pulisic.
The American went on to score the third in a 3-1 win that sent Lampard’s side to the top of the Premier League table, at least until Tottenham play Arsenal in the north London derby tomorrow.
However, the injury to Ziyech put a slight downer on a celebratory night, with fans back in attendance for the first time since March.
“With Hakim it’s a hamstring injury which we will find out the severity of in the next couple of days,” Lampard said. “The disappointment is going into this busy period.”
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