The tweet comes as WikiLeaks voiced its concerns regarding Assange's health following the news of the first confirmed COVID-19 death at the high-security Belmarsh prison where he is being held.
The WikiLeaks founder is currently awaiting a decision on his extradition to the United States. The hearings, which kicked off in February, were later adjourned until 18 May.
If Assange is extradited to the United States, he might face up to 175 years in prison.
Assange has been locked up for almost a year, ever since Ecuador revoked his political asylum and let the UK expel him from the Ecuadorian Embassy in London.