The band's frontman Chris Martin personally emailed Alex Lewis from Stockbridge, Hampshire, to say he had renewed his "faith in life", reported BBC online.
Rosemary Court, who helps manage Lewis's charity trust, said it had been "astonished" to discover the substantial donation from the band.
Court said the generosity had been "such a lift" for Lewis.
Lewis, a father, contracted a streptococcal infection which led to the rare Strep A Toxic Shock Syndrome.
His infected limbs were starting to poison his body and had to be amputated to save his life.