O'Brien, who joined the Leinster backroom team as contact skills coach following his retirement from professional rugby at the end of last season, had planned to play for Tullow in the Leinster League and the Towns Cup, however, his request was turned down by Leinster’s domestic committee.
Regulation 5.7 prevents any player from the professional ranks (excluding Academy) over the last two seasons from lining out in junior rugby, and due to the fact that O'Brien was still playing for London Irish last season, his return to Carlow has been put on hold.
According to the Leinster Rugby competition regulations: “All players who have played international (including 7’s), provincial, or professional rugby in any jurisdiction for the Senior full team, in the current or last 2 preceding seasons shall be ineligible to participate in any Competitions.
"This regulation does not apply to Academy contracted players who can play Under 20’s, Metro League Div 1, 2 or for any first team of a Junior Club."
O'Brien (35), who won 56 Ireland caps across a glittering career, has always been a strong advocate for Tullow rugby, but the regulation was seemingly introduced to protect junior players from coming up against recently retired professional athletes whose physicality would be viewed as a much higher standard.
That means for now at least, O'Brien's dream of pulling on his local jersey once again will have to wait.
O'Brien will be involved in his first competitive game as Leinster coach, when the side for whom he played 126 times, begin their URC campaign against Zebre in Italy on Saturday.