Cronk was on Friday ruled out of their round-two clash with Manly after experiencing hamstring tightness following their round-one loss to South Sydney.

The NRL granted the Roosters an exemption to include Lam, who wasn't included in their 21-man squad named on Tuesday.

The son of former Roosters halfback Adrian will make his first grade debut six months after re-signing with the club as the heir to Cronk's No.7 jumper.

It was tipped the 20-year-old would follow his dad to Wigan when the ex-Queensland representative took up the job over the summer.

Instead Lachlan was earmarked as the future after the club opted to allow fellow youngster Sean O'Sullivan to move to Brisbane.

The 35-year-old Cronk comes off-contract at the end of the year, however has made no final decision on whether he will hang up the boots.

Lam's shot at Lottoland will be an early litmus test for the defending premiers, who lost their season-opener to the Rabbitohs.

Speaking before news of Cronk's injury was announced, Robinson admitted his team were overly eager in their first outing of the season.

"There was actually excitement to get your footy on straight away and we wanted to do lots of things. It's about doing the really important things well early," he said.

Robinson also defended his team following criticism of their players following their heated battle with the Rabbitohs.

New signing Angus Crichton was branded a "traitor", centre Latrell Mitchell admitted to being baited, while Wayne Bennett called the Roosters "immature".

Robinson said he wanted his players to play within the rules of the game, but to also have the freedom to express themselves in their football.

"That's why people love watching our game. There's a presence to the way that guys play our game, and people know that," he said.

"People know there's a difference in some guys compared to others.

"You want to be able to express that.

"We've been focused on us. If you focus on other people too much at the start of the year and start talking about that stuff, you'll get lost."

The match marks the return of Des Hasler as Sea Eagles coach at Lottoland for the first time since 2011, where his side was undefeated in 10 matches.

Corey Waddell and Manase Fainu are in for Addin Fonua-Blake (suspended) and Trent Hodkinson (omitted) following their round-one loss to the Wests Tigers.

STATS THAT MATTER

- Manly have won five of their past eight against the Roosters.

- Their most recent meeting at Brookvale Oval in round 19 last year resulted in Manly conceding the equal most points at the ground in club history(56).

- Trent Robinson has won eight of his past 11 matches against Des Hasler, including games against Canterbury.

Australian Associated Press