Flyhalf Sexton returned to Racing Metro with his thumb in a splint this week following Ireland bruising 13-10 loss to England and the Parisian club said he would out of action for 10 days to six weeks.
However Ireland then issued a statement, saying that if Sexton continued his current rate of improvement, they were confident that he would be available for selection against Italy at the Aviva Stadium on Saturday.
Sexton was named in coach Joe Schmidt's extended 33-man squad on Sunday where he was joined by British and Irish Lions team mate Zebo, who was left out of Ireland's first three matches as he recovered from injury.
Hooker Richardt Strauss, who had heart surgery in October and was expected to be out for the season, also makes a welcome return while centre Luke Marshall misses out after suffering a concussion playing for Ulster on Friday.
Tommy Bowe, who played for the first time since November in the same game, scoring two tries, will continue to follow a staged return to action, the Irish Rugby Football Union (IRFU) said in a statement, explaining the winger's absence.
Ireland are in a four-way tie at the top of the standings but with a superior points difference. Victory over Italy would see them travel to France a week later where a win could seal their second championship in 29 years.
(Reporting by Padraic Halpin; editing by Toby Davis)
