Striker Michael Owen was carried off on a stretcher in the 67th minute of Newcastle's Premiership game with Watford.
The England international had collided with the shoulder of team-mate Matthew Pattison a couple of minutes earlier and was not fit to continue.
The injury-plagued £17million signing was playing just his 14th senior game for Newcastle since his 2005 transfer from Real Madrid.
The score was level at 1-1 at the time of the incident, with Marlon King's 52nd-minute penalty for Watford levelling the scores after Kieron Dyer had given Newcastle a 29th-minute lead.