Chelsea midfielder Mason Mount collected an ankle injury during their 4-4 draw with Champions League opponents Ajax.
The midfielder had to be replaced on 59 minutes by Callum Hudson-Odoi during the eight goal thriller.
The worrying thing for Chelsea is that it appears to be the same ankle he injured on his Champions League debut in September against Valencia.
Back then, he was clattered into by former Arsenal man Francis Coquelin and substituted.
There were initial fears that he had damaged ankle ligaments - but in the end it was discovered to be a sprained ankle.