Turnip was found weighing just 86kg on May 30 off Quibell’s Lane, Newark.
He was cared for by charity Help for Horses, who said he was "absolutely exhausted and very weak but is trying his best."
Janice Dixon, chair of the charity Help For Horses said: " This severely dehydrated, emaciated foal may have been there for a few days and when found was close to death."
The sad announcement was made by the charity today, June 3.
The announcement on social media said: "It is with heavy hearts that we have to tell you that Turnip has passed away.
"Turnip has tried so hard for four days and we thought he was making progress at the weekend as he was eating and drinking for himself and, once helped up, could stand unassisted.
"But unfortunately it was all too much for him and we will never know how long he’d been lying helpless in that field before he was found.
"We want something positive to come from his battle.
"Please watch our video and sign our petition to the government calling for enforced licensing on the breeding of horses, and a passport and microchip database system that is fit for purpose.
"Don’t let poor Turnip die in vain."