Brighton boss Graham Potter expects defender Shane Duffy to be out for a number of weeks with a calf problem.
The Republic of Ireland international was forced off during the closing stages of the 3-1 home Carabao Cup defeat by Aston Villa on Wednesday night.
Potter confirmed the centre-back would need more tests to determine how long he would be sidelined for, but appears a major doubt for the upcoming Euro 2020 qualifiers in mid-October.
"Shane is going for a scan, so we will see the extent of that," Potter said at a press conference ahead of the Premier League match at Chelsea.
"It looks like it is going to be weeks rather than days with him. It is a calf (problem)."
Potter had selected an inexperienced squad for the third-round tie against Villa due to injury and illness, including giving senior debuts to 10 academy players.
The Seagulls – who have not won in the Premier League since the opening weekend at Watford – had to be content with a goalless draw at Newcastle, despite what was a promising display.
Glenn Murray has resumed training after his ankle problem, so should be available for the trip to Stamford Bridge.
Forward Alireza Jahanbakhsh could come into contention after his time on the sidelines following an injury picked up during the last international break.
Potter, though, remains positive for the challenges ahead.
"Everyone has these moments. If you look at Newcastle, there were no excuses for anybody not being available," he said.
"In an ideal world of course you want everybody, but sometimes it is not to be and then you have to just make sure you are looking after them and they are getting back as soon as possible."
Potter added: "We are creating chances and are about where I expect us to be after six (Premier League) matches.
"But you get what you get and there is no point in feeling sorry for yourself.
"It's about making the best use of the group we have here and everyone's working really well.
"I am confident with the quality we have that it will turn around."
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