The 25-year-old, who joined the Exiles from Catalans Dragons last year, has made just one appearance for the club due to issues with his visa and a host of injuries.
Sa has revealed that he could have played on for the remainder of the season, but took advice from doctors before deciding to undergo the "minor" operation.
He tweeted: "Minor surgery needed so I'm good to go for pre-season and be hundred percent for next season. Could of carried on but medics' choice."
Sa is a full international for Samoa.