Alexander Isak was replaced on Tuesday when Newcastle won 2-1 against Southampton and went on to the final in the League Cup.
However, the Swede was forced to abandon the match after receiving a hard free kick from James Ward-Prowse in the head just before full time.
The 23-year-old fell to the ground but got up and tried to play on.
But in added time he was replaced after continuing problems with his head.
Now the Swede comes with a reassuring message on social media.
"Stepped off with a minor head injury but I'm fine under the circumstances," he writes on Instagram.
The Swede has previously missed most of the autumn due to injury.
The final, which will be played at Wembley on February 26, pits Newcastle against Manchester United or Nottingham.