Charlie Boyle, 23, from Paisley, was babysitting for the young boy at his home in Neilston,Glasgow, when he tossed him up three times.
The baby was rushed to hospital after becoming floppy and unresponsive.
The High Court in Glasgow heard that Boyle had earlier been warned by the baby's mother about throwing the child in the air.
Boyle insisted he was just playing with the child, who he claimed was “laughing”.
Medical experts said the child, who cannot be named for legal reasons, may have died, but for urgent medical help.
Boyle pled guilty to culpably and recklessly throwing the boy to his severe injury and to the danger of his life at a house in Neilston, Glasgow, on June 5, 2017.
He was initially accused of attempting to murder the child, but halfway through the trial prosecutors accepted his plea to the reduced charge.
Judge Lord Clark told Boyle: “It should have been obvious to anyone this could cause the baby's head to flop forward or backward causing injury.
“When the baby was rushed to hospital you initially did not say what you had done.
“Very fortunately the child, who is now two, is meeting all his developmental milestones. I accept you have expressed remorse and I also accept you did not mean to deliberately assault the baby, however you placed his life in danger.
In evidence the boy's mum told the High Court in Glasgow: “Charlie was good with kids.”
However, it emerged she had previously warned Boyle not to throw the baby into the air.
A distressed Boyle called his own mother on the day of the incident “crying and upset” stating the boy “was not moving”.
The ill child was rushed to intensive care suffering from bleeding near the brain, the eyes and also suffered seizures.
Prosecutor Ashley Edwards QC said: “A doctor has confirmed the child's life was in danger and, without medical treatment, he might have died.”
The boy recovered, but will continue to be monitored by doctors.
Another doctor stated “significant trauma” would have been needed to cause the injuries.
Boyle told police he had been playing with the child while the baby's mother was out.
Miss Edwards: “He advised he had been throwing the boy up into the air before catching him.
“He described his actions as not having hold of the child before he caught him.
"Boyle stated the boy had been enjoying this and laughing.”
The court heard he told officers of doing this “three times” before the child started crying and his eyes closed.
Boyle the baby was tired and put him in his pram, but he soon began making “squeaking noises” and appeared “lifeless”.
Miss Edwards: “He told officers he was too scared to tell hospital staff that he had thrown the child in the air as he would 'get blamed and get the jail'.”
Defence QC Edward Targowski urged Lord Clark not to jail Boyle saying: “If Mr Boyle is given a custodial sentence there is no guarantee he will receive any help for the problems he has. It will not make him a better person.
“Thankfully the injuries to the child are not life changing and hec is meeting his milestones.
"Mr Boyle has expressed remorse for the injuries he caused.”