Gagai, 30, is returning to the Knights on a three-year deal after the 14-12 defeat in his first NRL grand final.

The Queensland Origin star was one of the Rabbitohs' best in the thriller at Suncorp Stadium, breaking 10 tackles, making their most runs (17) and carving out 110 metres, despite missing 13 minutes because of an early head injury assessment.

The centre's gains included 34 post-contact metres and he also threw the final pass for Alex Johnston's try in the 74th minute which gave Souths a chance to level.

Zammit was impressed with Gagai's hard yards as Souths struggled for decent field position against the kicking game of Clive Churchill medallist Nathan Cleary.

"I thought he was good, I thought he competed well, which is what he will bring to us," Zammit said.

"He's tough and he's a professional, so that will be wonderful for us.

"Souths had to come out of their own end all night, and their back three got manhandled a bit, so I thought he was good. He made some strong carries for them.

"With his carries last night, he's a tackle-breaker too. The way the game is going, it's important to have some tackle-breakers in your team to get some momentum, and he'll definitely give us that."

He said Gagai would also play a crucial role at training in setting the example for players like exciting prospect Krystian Mapapalangi.

"He will be good for us, not only with what he brings on the field but off it as well," he said. "He's a pro off the field and he will help a couple of those younger kids we've got coming along in learning how to train and how to be a professional. He looks after his body and does all the right things, and he hasn't slowed down at all, which is a good sign."