Tom Brady sent a heartfelt message to Ryan Mallett and his family after the former quarterback tragically died on Tuesday ... writing in a sweet note, "We lost a great man."
The Patriots legend -- who was teammates with Mallett in New England from 2011 to 2013 -- posted the message to his Instagram page ... adding, "Thank you for everything Ryan."
"Praying for the Mallett family and all their loved ones tonight."
The post went up only hours after cops say Mallett drowned while swimming in the Gulf of Mexico on Tuesday afternoon.