Junior doctor Matt Smith, 28, was on his way home from work at Leytonstone station when he heard people shouting there was a knifeman on the loose.
Matt rushed down the stairs to be confronted by a man grabbing his neck, surrounded by a pool of blood.
He said: “The man was clutching at his neck and there was lots of blood on the floor and it looked like there was nobody there trying to help him.
“I ran down the stairs and tried to help, he had a big slash wound on his neck and there was a man next to him trying to use his jumper as a bandage trying to stop the blood.
“We just tried to keep pressure on the wound and to make sure he was conscious. I thought he was going to pass out and I was going to have to start CPR.
“I had a quick look at the wound, it was horrendous so we quickly put the pressure back on and then unfortunately the attacker came back.