In the pre-season Grevsmuhl played in the Rabbitohs' Auckland Nines winning campaign, the Charity Shield, and scored a try on debut for the Indigenous All Stars in the annual All Stars match. In Round 1, he made his NRL debut for the Rabbitohs against the Brisbane Broncos. In Round 4 against the Parramatta Eels, he scored his first NRL try in the 29-16 loss at Parramatta Stadium. In Round 12 against the Gold Coast Titans, Grevsmuhl scored his first double in the 22-16 win at Cbus Super Stadium. He finished his debut year in the NRL with 6 tries from 22 matches and was awarded with the 2015 John SattlerRookie of the Year award. On 7 October, he re-signed with the Rabbitohs on a 1-year contract.
2016
In January, it was revealed that Grevsmuhl had signed a 2-year contract with the Penrith Panthers starting in 2017. Selected in the QAS Emerging Origin squad, on 5 February, he was one of eight players from the Maroons emerging camp who was banned from representing Queensland for 12-months after breaking curfew in Brisbane. He was selected to play for the Indigenous All Stars, but withdrew before the match. On 20 May, Grevsmuhl joined the Panthers mid-season after being released from the remainder of his Rabbitohs contract. He said that he was unwilling to play under Rabbitohs coach Michael Maguire any further. Grevsmuhl said, "He’s a mind-game specialist. He breaks you down mentally. He questioned why I was there, the effort I was putting in, and questioned why I was talking to other clubs. On 25 November, Grevsmuhl was granted an immediate release from his Panthers' contract on compassionate grounds.
2017
In March, the Gold Coast Titans announced the signing of Grevsmuhl for the 2017 and 2018 seasons. On 2 April, Grevsmuhl made his Titans debut, coming off the bench in the 28-22 loss to the New Zealand Warriors. He scored his first try for the Gold Coast in the 24-22 loss to the Brisbane Broncos in Round 7. After being unable to play for the remainder of the 2017 season due to a shoulder injury, the Titans released Grevsmuhl on 11 August after only four games with the club. The same day that he was released from the Titans, it was reported by various media outlets that Grevsmuhl took payment from fans for a number of his jerseys, but never delivered the goods. This incident led to the Titans stepping in and paying out the fans who were left out of pocket, and returning the payment from Grevsmuhl's salary. The Titans refused to comment whether or not this was the reason that they released Grevsmuhl.
2018
In March 2018, Grevsmuhl signed a one year contract to join Group 10 country rugby league side CYMS Orange.
2019
During November 2019, Grevsmuhl was back spotted training with the South Sydney Rabbitohs, however Shane Richardson said they had no interest in signing him.