West Ham made the first concussion substitute in English football during their FA Cup fifth-round game at Manchester United.
Issa Diop - himself an early replacement for the injured Angelo Ogbonna at Old Trafford - clashed heads with Anthony Martial towards the end of a goalless first half.
Ryan Fredericks emerged for the second period and West Ham announced via their Twitter account that the change was a concussion replacement.
Last month, the Premier League and the Football Association approved a trial allowing teams to make a maximum of two additional substitutions in the event of players suffering head injuries and showing symptoms of concussion.
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Last weekend was the first time Premier League clubs had the option of making such changes, although none were required.
Teams participating in the Club World Cup can also make concussion substitutions, although FIFA is allowing just one additional change.