Top tier and EFL football has been suspended since March 19 in a bid to curb the spread of the virus.
London has been badly hit by the pandemic and City Hall, working alongside NHS colleagues, believes football clubs can help with providing access to facilities, accommodation and clinically trained personnel.
Many are already working in the community and Sadiq Khan has written to nine clubs across the top two divisions in the capital to ask to support the NHS during these "unprecedented times".
"London is currently at the forefront of the UK's response to slow the spread of coronavirus, and the Greater London Authority (GLA) is working hard to help support the NHS in London," the Mayor of London wrote to clubs.
"Whilst the NHS is currently doing a fantastic job in responding to the crisis, NHS staff are already feeling the additional strain and that is why we need to give them the time, space and support they need to save the lives of Londoners.
"I am clear that I will do everything I can to support the capital during the coronavirus crisis and that means giving the NHS the vital resources it needs to treat those in need. This is where I hope football clubs across London will be able to help."
Khan added: "I do not take such requests lightly and I appreciate that this is a big ask in what is currently a challenging and uncertain time for many of London's football clubs.
"However, I am clear that we all need to unite and do what we can to support the NHS and protect the lives of Londoners in these most challenging of circumstances."
Tottenham did not receive a letter in this round as they are already working with City Hall, while Watford were not contacted as they are just out of the Greater London area.
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