Anelka had announced on Twitter he planned to terminate his contract with the Premier League club, just a day after it was confirmed he would accept a five-match ban for making a quenelle gesture.
The club said Anelka, who turned 35 on Friday, was unwilling to agree to conditions they set, which may have allowed him to resume training.
West Brom wanted Anelka to apologise for the gesture – associated with anti-Semitic sentiments – he made in December, and accept a 'substantial fine'.
"Nicolas Anelka's purported termination of his Premier League contract this evening via social media was invalid as this was not conducted under the correct legal process as required by his contract," the club said in a statement.
"The club considers the conduct of Nicolas Anelka on December 28, coupled with his purported termination on social media this evening, to be gross misconduct.
"As a result the club has tonight written to Nicolas Anelka giving him 14 days' notice of termination as required under his contract."
Anelka decided on Thursday against contesting a five-match ban and £80,000 fine handed to him by the Football Association.
He said the salute was devised by his friend Dieudonne M'bala M'bala and an anti-establishment gesture.
The FA accepted Anelka was not an anti-Semite, but the gesture was.
