West Brom say Nicolas Anelka will never again perform the gesture that has been regarded by some as anti-semitic.
The Frenchman flashed a sign known as the quenelle that can be considered as a reverse Nazi salute after he scored in Saturday's draw at West Ham.
It has caused a storm in his homeland.
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The club say the player "strongly" denies intending to cause offence, although he revealed that his gesture was in support of controversial French comedian Dieudonne who popularized the symbol.
The Football Association is investigating and Anelka could receive a ban.