Mason Mount was yet to even feature for Chelsea’s senior side six weeks ago. But it is a testament to just how brightly he has started this season that his injury against Valencia, inflicted by Francis Coquelin’s reckless challenge, came as a considerable blow to manager Frank Lampard.

There were just nine minutes on the clock in the Champions League Group H clash at Stamford Bridge when Coquelin planted his studs onto Mount’s right leg, causing the 20-year-old’s ankle to turn unnaturally. He tried to run it off, but it soon became clear that he would not be able to continue. Mount trudged down the tunnel and a significant chunk of Chelsea’s attacking threat went with him.

Mount limps off early on CL debut

The game was ultimately decided by the slack marking which allowed Rodrigo to plunder Valencia’s winner and Ross Barkley’s failure to convert from the penalty spot in the closing stages, but Mount’s absence was also significant. “Obviously it was a shame because he was playing so well and he had started the game well,” said Lampard afterwards.

Mount’s goal in the 5-2 thrashing of Wolves on Saturday was his third in his first five games of the season. As well as providing a scoring threat from midfield, the academy product has become Chelsea’s attacking spark, stepping into the void left behind by Eden Hazard and creating more chances and taking more shots than any of his team-mates.

Chelsea missed that guile on Tuesday night. Lampard chose Pedro as Mount’s replacement, citing his Champions League experience afterwards. But while the 32-year-old was typically industrious out of possession, he had not featured at all since Chelsea’s 1-1 draw with Leicester a month ago and his rustiness was evident at Stamford Bridge.

There were groans of frustration from the home supporters as attacks broke down around him in the first half. Pedro offered little in the way of creativity – his struggles summed up by one late cross which failed to beat the first man – and he spurned his only clear sight of goal when he curled a shot harmlessly wide shortly before Valencia’s winner.

Chelsea did create openings, but Valencia were untroubled by the majority of their 22 shots and the hosts were generally reliant on moments of individual skill from Willian. The Brazilian ran rings around Valencia’s defenders at times, but he lacked the kind of clinical edge Mount has provided recently and is still waiting for his first goal or assist this season.

Rodrigo Moreno celebrates scoring Valencia's winner on Tuesday night Rodrigo Moreno celebrates scoring Valencia's winner on Tuesday night Rodrigo Moreno celebrates scoring Valencia’s winner on Tuesday night

Chelsea’s 3-4-2-1 formation allowed Cesar Azpilicueta and Marcos Alonso to bomb forward from the wing-back positions, but they too struggled to deliver in the final third. Between them, and despite repeatedly finding themselves in good positions, they completed just two crosses out of nine.

Why Pulisic will need time too

Tammy Abraham battled gamely up front, winning all six of the aerial duels he contested and sending one header narrowly wide, but he missed Mount’s service as much as anyone. Lampard admitted Chelsea “did not create a lot of fantastic chances” in his post-match press conference. When they needed a flash of ingenuity, it wasn’t there.

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Lampard added that it was too soon to judge the seriousness of Mount’s injury, saying Chelsea will wait for scans to find out the full extent of the damage. But the nature of the challenge makes it worrying and the timing is unfortunate – not just because of his form but because of what’s to come.

Chelsea welcome Liverpool to Stamford Bridge on Super Sunday and after that, they have four games in the space of 12 days – including a trip to Lille in their second Champions League group stage fixture. It is a hectic period and an inopportune moment for Lampard to be deprived of a key player.

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Frank Lampard says Chelsea will assess the extent of Mason Mount's injury

Frank Lampard says Chelsea will assess the extent of Mason Mount’s injury

All the more so given he is not currently confident calling on Christian Pulisic. The USA international, a £58m signing from Borussia Dortmund before Chelsea’s transfer ban took hold in the summer, was left on the bench for Saturday’s win at Wolves and it was the same story against Valencia, despite Mount’s withdrawal and Chelsea’s struggles in attack.

It should come as no great surprise that a 21-year-old Premier League newcomer is taking time to adapt to his new surroundings – and Lampard insisted Pulisic is “well in his plans” after the game – but Chelsea will need him to be ready if his team-mate’s injury turns out to be serious. It is only six weeks since his Chelsea debut, but Mount is already vital to this side.

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