The back-row forward was sent to see a specialist over the injury and it was decided a "small procedure" was needed but it looks like it means he will be ruled out of at least the first Six Nations game for Ireland this year.
"Sean O’Brien saw a specialist this week for the tightness in his hip as it hadn’t responded to treatment as we would have liked," a Leinster statement read.
"As a result he had a small procedure and the target is to have O’Brien back available during the Six Nations window."
Ireland begin their Six Nations campaign in France on February 3 and it looks like O'Brien will be absent for the opener, and possibly the second game against Italy on February 10.
O'Brien has not played since Leinster's last Champions Cup game, a win over Exeter on December 16, due to the injury.