Francis Jeffers, who also played for Arsenal, Everton and England, pleaded guilty to sending offensive and menacing messages to his wife Lucy at Liverpool Magistrates' Court on Wednesday, a spokesman for the Crown Prosecution Service (CPS) said.
The CPS said Jeffers, 38, sent the WhatsApp messages after their 20-year relationship broke down and he became convinced she was having an affair.
He told his estranged wife, 38, that her life was over and she would not need many of her clothes as she would be in a coffin.
Jeffers pleaded guilty to sending an offensive and menacing message and was fined £625, ordered to pay £85 costs and a £62 victim surcharge, the CPS said.
A 12-month restraining order was imposed to stop him contacting his ex-partner.
X-Factor star Danny Tetley appears in court charged with multiple child sex offencesPawel Relowicz appears in court charged with murder of Hull university student Libby SquireCrown prosecutor Sophie Leyland said: "Francis Jeffers has had an impressive career as a professional footballer and is a coach with Everton FC.
"But he has embarked on a course of action that has now brought him before the courts and sent his wife menacing messages that left her genuinely fearing for her life.
"His motivation for sending the messages is irrelevant - to send messages like that is a criminal offence and he has caused his wife real distress."
Jeffers, who is widely regarded as one of the Owls' worst signings ever, scored just five goals in 54 appearances after signing for an undisclosed fee, believed to be around £800,000, from Everton in 2007.