Ian King, 45, had suffered pains in his calves and feet for some time before going to hospital to get them checked out when he returned from holiday in April.
A blood clot was found and doctors operated to remove it.
Ian was put on a drip but suffered a rare reaction to the blood thinning medication he was put on and it actually made his blood thicken.
A new clot formed and doctors said that they would have to remove his leg because of the damage, revealing later that he was only a few minutes away from dying.
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“They told me at 3pm, then at 3.20pm they took my leg off,” said Ian, of Coultons Avenue in Sutton.
“I went from being a fully able person ready to go back to work after my holiday to losing a leg. There was no time to adjust.”
Dad-of-two Ian is well known in Kirkby having been a postman there for 13 years, but having his leg amputated has completely changed his life.
He hopes to return to work at Royal Mail in a different role but now finds getting around much more difficult.
His friends and colleagues are therefore on a fundraising drive to raise £4,000 to buy Ian a lightweight titanium wheelchair.
Vicky Lee, wife of fellow postman Paul, is spearheading efforts.
Vicky, 51, of Beverley Drive, Kirkby, said: “I love raising money for people to help them.
“Ian is a good buddy of Paul’s and they have a good connection.”
Nearly £3,000 has been raised by a sponsored 13 mile walk that friends and colleagues completed around the Chatsworth Estate in Derbyshire.
Now a fundraising evening is being held at Kirkby Catholic Club, on School Street, on Saturday, October 10 from 6.30pm until midnight.
Featuring lots of games and fun activities, plus a disco, tickets are £3 for adults and £1 for children and are available from Paul at Kirkby Sorting Office or from Vicky on 07946 086565.
Ian said: “The wheelchair will make a massive difference to me. It will give me a lot more independence.”