Both Herbert and McCrone are off contract at the end of the season and the club plans to retain just one of them.
With Buttriss a chance of making next week's trip to New Zealand, Herbert will need to have an immediate impact against the Rabbitohs to make up ground on McCrone.
Raiders chief executive Don Furner admitted the time to pick a halfback for next season was nearing.
"We've talked about sitting down ... in maybe round nine or 10 and seeing how each was going," Furner said.
"We're only through round six, but within the next month we'll sit down with the coaching staff and talk about that."
Don Furner said the club would make some tough retention and recruitment decisions in the coming weeks.
"The next six to eight rounds is always difficult," he said.
"It's an unusual industry that you're tapping someone on the shoulder and saying 'I'm sorry you aren't with us next year, but can you please play your guts out for us?'.
"... Negotiations for the retention of some players I hope that proceeds soon and goes well."
The Raiders remain eager to recruit Cowboys forward James Tamou, while veteran prop Scott Logan is rumoured to be having second thoughts about retirement.Other notable players off contract include winger Justin Carney and utility Danny Galea.
Furner also met with fullback Josh Dugan's manager last week.
The Raiders are desperate to immediately extend the future representative's contract beyond 2011 to ward off rival clubs such as the Sydney Roosters.
"It's been dragging on for a long time and it's frustrating," Furner said.
