South Sydney's coach is optimistic a lower-back issue will only keep in-form Mitchell sidelined from Saturday's clash against Cronulla at Accor Stadium.
Mitchell hurt his back at half-time of the round-nine clash against Newcastle, and Bennett said the star was "close to tears" due to the pain.
The 28-year-old played through the significant discomfort and was man of the match as the Rabbitohs' comeback fell just short in the 42-38 loss.
At worst, the coach said Mitchell could miss a fortnight with a bulging disc in his back, which would rule him out of the Magic Round clash against Bennett's old side the Dolphins.
But Laurie Daley will not name his NSW team until after that weekend, meaning Mitchell should be fit in time for the Origin series opener in Sydney on May 27.
"No, I don't think he's in doubt (for Origin)," Bennett said on Friday.
"He's got some treatment for it, got a needle yesterday or the day before, he reacted pretty well to it all.
"I won't push for him to play if he's not fit, but State of Origin's two and a half weeks away at least, so he'll certainly be right by then.
"No doubt about that."
Bennett said the club had been hopeful Mitchell's injury would have settled in time for teammate and close friend Campbell Graham's 150-game milestone.
"He told me he was in a lot of pain (during the Newcastle game) and I asked him if he could carry on, he said he could," Bennett said.
"He got home and the following morning he could hardly walk, so he's been in a fair bit of pain most of the week.
"We all hope it'd kind of settle down a bit quicker than it did, but he got a scan and then got an injection, and it's settled down a lot more now since that's happened.
"It's only a small setback, so nothing major."
There will still be a Latrell in the Rabbitohs line-up, with youngster Siegwalt to make his NRL debut in Mitchell's place.
Siegwalt, 25, is one of four new faces in the starting line-up for the fourth-placed Rabbitohs.
"He's a bit of a star in the State League in Queensland," Bennett said of Siegwalt.
"He's been great to work with, he's a very good athlete, very good, highly skilled.
"He's got an opportunity, and I'm pleased for him."
A fit-again Jye Gray (shoulder) will replace Matt Duffy at fullback, while playmaker Jamie Humphreys (leg) will join Mitchell on the sidelines.
Humphreys had initially been benched to accommodate Ashton Ward's return from an ankle injury at halfback, but now drops out altogether.
Former Warriors back Ed Kosi will make his club debut in place of Jack Wighton, who broke his arm against the Knights.
Souths are preparing for a Cronulla outfit riding high from a 52-10 shellacking of Wests Tigers.
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