Ireland prop Marcus Horan will miss this month's Tests against Australia, Fiji and South Africa in Dublin and is not expected to play again until the New Year.

The Munster forward has undergone what an Irish Rugby Football Union (IRFU) statement on Friday said was a "routine medical procedure".

The frontrower left the pitch after 17 minutes of Munster's European Cup win over Italian side Treviso nearly three weeks ago after saying he felt dizzy.

Concerns were raised over the 32-year-old Horan's future but the IRFU statement said the 66-times capped front row would be back in action within eight weeks.

"It has been confirmed that Marcus will not be available for the Guinness Series games," the statement said. "Following further tests this week, Horan underwent a routine medical procedure today (Friday) and will undergo a period of rest over the next number of weeks.

"It is expected that he will be available to Munster and Ireland after the New Year."

Horan was left out of the 31-man squad the Six Nations champions announced Friday for next week's Test against Australia.

But Munster hooker Jerry Flannery was included after making progress in his recovery from a calf problem.

And with Rory Best out for the season with a neck injury, Sean Cronin and John Fogarty have been retained in Ireland's senior squad to provide cover should Flannery be forced to pull out.

Tomas O'Leary and Eoin Reddan will compete to be the Six Nations champions' first-choice scrum-half with veteran No 9 Peter Stringer included among a 22-man Ireland 'A' squad for their match against Tonga at Belfast's Ravenhill ground a week on Friday.

Australia begin their quest to complete a grand slam of wins over all four 'Home Nations' (England, Ireland, Scotland and Wales) on the one tour when they face England at Twickenham on Saturday.

Ireland squad for their one-off international against Australia at Croke Park on November 15 (1500GMT):

Backs: Tommy Bowe (Ospreys/WAL), Gordon D'Arcy (Leinster), Ian Dowling (Munster) Keith Earls (Munster), Luke Fitzgerald (Leinster), Denis Hurley (Munster), Felis Jones (Munster), Robert Kearney (Leinster), Brian O'Driscoll (Leinster, capt), Ronan O'Gara (Munster), Tomas O'Leary (Munster), Eoin Reddan (Leinster), Jonathan Sexton (Leinster), Paddy Wallace (Ulster)

Forwards: Bob Casey (London Irish), Tom Court (Ulster), Sean Cronin (Connacht), Leo Cullen (Leinster), Stephen Ferris (Ulster), Jerry Flannery (Munster), John Fogarty (Leinster), John Hayes (Munster), Cian Healy (Leinster), Jamie Heaslip (Leinster), Denis Leamy (Munster), John Muldoon (Connacht), Donncha O'Callaghan (Munster), Paul O'Connell (Munster), Mick O'Driscoll (Munster), Niall Ronan (Munster), David Wallace (Munster)