Witnesses said the 62-year-old Ahern was attacked at a bar Friday by a middle-aged man wielding a crutch.
He has also been the subject of two incidences of verbal abuse and intimidation on his way to and from another pub he has frequented for many years in his native Drumcondra, the Irish Independent reported.
Ahern, who led the Fianna Fail party to three successive general election victories between 1997 and 2007, stepped down as prime minister -- or taoiseach -- in 2008 following allegations of bribe-taking made at a tribunal investigating corruption in Dublin.
During his time in office, Ahern was regarded as one of Ireland's most successful prime ministers, serving as the country's leader as it enjoyed a decade-long economic boom known as the Celtic Tiger era.
After his departure, however, the nation suffered a catastrophic recession that has been partly blamed on Fianna Fail's policies of lax banking supervision, fueling a real estate bubble.
In 2010 Ireland received a $113 billion bailout from the European Union and the IMF and has since been subjected to harsh austerity measures.
Ahern has taken the blame from the Irish public, which is still suffering with an unemployment rate of 13.4 percent.
In the Friday incident, Ahern was at the Sean O'Casey Pub near the Abbey Theater in central Dublin when he was attacked by Ray Connolly, who admitted to the Irish Independent he took a swing at the former taoiseach with his crutch.
Connolly said the former politician was "laughing all night long" and he became upset when he heard Ahern say, "That was in the good old days," before bursting out laughing again.
"He's put a lot of people in a terrible situation," Connolly told the newspaper.
A witness said the crutch missed Ahern, instead connecting with a counter.
Connolly was arrested and taken to a police station where he was charged with a minor offense, the newspaper reported.
Friends of the former PM told the Independent he was also the subject of hate mail in the form of a rope sent to his Dublin home, with the suggestion he hang himself with it.
Although Ahern was described as "unfazed," the incidents have reportedly prompted calls for Ahern's security arrangements to be reviewed.
The attacks came even as Ahern was warmly praised by former British Prime Minister Tony Blair for his key role in negotiating the 1998 Good Friday agreement on power-sharing in Northern Ireland.
In the foreword of a new book of diaries written by aide Alastair Campbell, Blair wrote, "We were immensely fortunate to have an Irish leadership -- in the form of Bertie Ahern and his key ministers -- that was prepared to lay aside the grievances and attitudes of the past in the interests of the future."