Animal charity the RSPCA has taken West Ham defender Kurt Zouma's pet cats away after videos emerged on social media of him kicking and slapping one of them.
The Royal Society for the Prevention of Cruelty to Animals is liaising with Essex Police about the incident.
"The two cats are now in RSPCA care," said a charity spokesperson.
The Premier League club say they have fined Zouma "the maximum amount possible" and the fee will be donated to animal welfare charities.
German sportswear firm Adidas announced on Wednesday it had ended its deal with the 27-year-old.
"We have concluded our investigation and can confirm Kurt Zouma is no longer an Adidas-contracted athlete," said the company.
Also on Wednesday West Ham sponsor Experience Kissimmee said "due to recent events" it would end it's deal with the club.
More than 150,000 people have signed an online petition calling for Zouma to be prosecuted, while one of West Ham's sponsors, Vitality, has suspended its deal with the club.
West Ham said Zouma "willingly complied with the steps taken in the initial stage of the process, including delivering his family's two cats to the RSPCA for assessment".
The RSPCA spokesperson added: "Our priority is and has always been the wellbeing of these cats.
"They've been taken for a check-up at a vets and then will remain in our care while the investigation continues.
"We're grateful to everyone who expressed their concern for these cats. We were dealing with this issue before the video went viral online and are leading the investigation.
"We continue to investigate so we cannot comment further at this time."
The Hammers said the fine, which Zouma immediately accepted, was "separate to the RSPCA's investigation and pending further sanction once the outcome of that process is determined".
They added: "Kurt is extremely remorseful and, like everyone at the club, fully understands the depth of feeling surrounding the incident and the need for action to be taken.
"West Ham United would like to reiterate our condemnation of Kurt's actions and make it clear that the matter continues to be handled with the utmost seriousness.
"However, we believe it is now important to allow the RSPCA to conduct their investigation in a fair and thorough manner, and will be making no further comment at this stage."
West Ham manager David Moyes played France international Zouma in their match against Watford on Tuesday, despite the controversy, and the centre-back was booed by both sets of supporters during the game.
BBC Sport presenter and ex-England international Gary Lineker said he was "shocked and appalled that West Ham played Zouma" against Watford and called it a "tone-deaf decision".
BT Sport pundit Joe Cole, who used to play for West Ham, called the decision a "miscalculation".
'They clearly think they can get away with it'
One of West Ham's sponsors, Vitality, said it was "distressed" by the video of Zouma and "hugely disappointed by the judgement subsequently shown by the club in response to this incident".
The company added: "As such, we are suspending our sponsorship of West Ham United with immediate effect. We will now be further engaging with the club to understand what actions they will be taking to address the situation."
The West Ham Supporters' Trust (WHUST) has said it "condemns the actions" of Zouma. It is understood the trust feels Zouma should have been suspended until club disciplinary procedures had been concluded.
"I think it was an unwise choice to make [to pick him against Watford]," said WHUST chair Sue Watson. "Kurt Zouma is a good player, I understand why he chose him but I think he shouldn't have.
"He should have taken a moral stance and said, 'until the internal investigations and disciplinary procedures at West Ham are completed, he won't be picked'.
"Whether they do cast him aside - I strongly suspect they won't - I would like to see a very rigorous re-education programme. He's said he's sorry, I wonder if he understands why people are so angry with him."
Speaking to BBC Radio 4's Today programme, wildlife television presenter and conservationist Chris Packham described Moyes' decision to play Zouma on Tuesday as "disgraceful" and said the manager "proved he doesn't care" about the public standards footballers set.
"It's not acceptable," said Packham.
"We cannot condone this behaviour. West Ham should have sent a clear message. People were disgusted by this. Fans were booing. The decision shows a complete disconnect from them.
"This isn't an internal matter. It's a crime. They clearly think they can get away with it because it's an animal and not a person.
"Look at Marcus Rashford - he's a paragon of excellence - a true role model. There's potential that kids will see how Kurt Zouma treats defenceless animals and want to emulate him."