A lawyer for the family of Sergei Magnitsky, the lawyer whose death in 2009 sparked a crisis between Russia and the West, has been badly injured.
Russian media say Nikolai Gorokhov fell from the fourth floor when a rope snapped as he and others tried to lift a bathtub into his house near Moscow.
He was flown to hospital by helicopter, a medical source was quoted as saying.
However, British businessman Bill Browder, for whom Mr Magnitsky worked, said he had been "thrown".
He did not give a source for his allegation.
According to a press release released by a website linked to Mr Browder, Law and Order in Russia, Mr Gorokhov was due to appear in an appeals court in Moscow on Wednesday to contest its refusal to investigate allegations of organised crime.
Mr Magnitsky died in prison after revealing alleged fraud by state officials.
The incident involving Mr Gorokhov occurred in the town of Troitsk, south-west of Moscow. Russian media said several workmen were helping the lawyer at the time.
Footage on Russian media showed pictures of the tub and the debris of a wooden structure beside it.
One man described as a witness told Russia channel NTV that a delivery company had offered to carry the tub up to the fourth floor but that Mr Gorokhov had said he would winch it up the side of the building himself.
"He tried to use a homemade mechanism to lift it to the fourth floor. While he was doing that the winch got jammed. He went to fix it a bit and fell, with the jacuzzi and the makeshift scaffolding which landed on top of him," he said.
His comments appeared to indicate the workmen were on the ground at the time of the accident.
Who was Sergei Magnitsky?
Mr Magnitsky was jailed after being accused of committing fraud himself. Supporters say his death in November 2009 was the result of a severe beating, but official records say he died of acute heart failure and toxic shock, caused by untreated pancreatitis.
Mr Magnitsky had acted as a legal adviser for London-based Hermitage Capital Management, founded by Mr Browder (formerly a US citizen), who was himself tried in absentia.
The Magnitsky affair soured relations between Moscow and Washington, casting a spotlight on corruption in Russia.
It led to US sanctions on a group of Russian officials, retaliation by Russia and the bizarre spectacle of Mr Magnitsky being put on trial posthumously.