Alex Smithies is being assessed after being withdrawn in the opening stages of Cardiff City's clash with Bristol City.
The goalkeeper needed medical treatment in the ninth minute of the Championship fixture at Ashton Gate.
Following a significant break in play - during which Smithies was attended to by members of Cardiff's medical staff - the 30-year-old was replaced by Dillon Phillips.
He was carried off the pitch on a stretcher and was sitting upright when taken off the field of play.
The Bluebirds' official Twitter account posted on Twitter: "Alex Smithies receiving treatment. No involvement in play. Looking like he'll be unable to continue."
They followed up that post by confirming that Smithies had been replaced.
"Dillon Phillips replaces Alex Smithies. Thinking of you, Alex," they wrote in a separate tweet.
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