The 21-year-old has not played for the Scottish Premiership champions since January due to a knee injury.
The centre-back - who cost £5m in the summer (via The Scottish Sun) - has not played for the Hoops since late January due to a knee injury, and while Ronny Deila had hoped that he would have been back for early April, a setback in his recovery appears to have added another couple of months onto the time he is expected to be out for.
The Scottish Sun reports that despite appearing to be on his way back, Simunovic was still struggling and it was decided that surgery would be the best course of action, meaning that he could now be up against it trying to prove his fitness in time for the Bhoys' European qualifiers for next season.
The news that the 21-year-old is set to sit out the rest of the campaign may dent Deila's hopes of leading Celtic to a league and cup double this term.
While the Croatian's season has been blighted by injury, when he has played, he has been impressive so the Hoops boss may have hoped to have had him available to help them ensure that they close the door on Aberdeen in the title race - Celtic boast a four point lead at the top of the table, and have played a game less - and go on to win the Scottish Cup, which would involve having to overcome Rangers in the semi-final.