Olakau'atu was sin-binned early in the second half of the Sea Eagles' 34-26 loss at Leichhardt, for a shot on Tigers fullback Heath Mason.
While off the field, the Tigers ran in two crucial tries to go from 16-10 down to 22-16 up.
Replays of the hit appeared to suggest the contact had been shoulder on shoulder, but referee Peter Gough deemed it worthy of a sin-bin.
The match review committee opted for a lower-end sanction on Friday, handing Olakau'atu a grade-one charge and $3000 fine with an early guilty plea.
The NSW State of Origin second-rower was one of three Manly players sin-binned in the loss, with Ethan Bullemor also marched for repeated offences.
Bench forward Corey Waddell was sin-binned late for a high shot on Solomon Alaimalo, and is facing a two-match ban for the grade-two high tackles.
Manly forward Taniela Paseka is also facing a $1000 fine for his role in the same tackle.
Thursday night's shock loss after leading 16-0 early hit Manly hardest on the ladder.
A win over Canterbury or Cronulla in the next fortnight, or a Dolphins loss to Melbourne, Brisbane or Newcastle will be enough to see Manly progress to finals.
But they now face a battle to regain a home final with a top-six finish, while their top-four hopes are all but shot.
Corey Waddell was one of three Manly players sent to the sin bin in the costly loss. (Dan Himbrechts/AAP PHOTOS)
Manly coach Anthony Seibold said he would give players 24 hours to stew on their loss to the last-placed team, when six first-half penalties and a glut of errors hurt them.
"You get what you deserve in the NRL. We've deserved some really good results because we've played some really good footy but tonight we weren't there," Seibold said.
"We'll go back and prepare well because we've got a big game against the Bulldogs next Friday night. We know how well they've been playing."
The Sea Eagles had won five of six games prior to their round-25 loss but are yet to face either the Bulldogs or Sharks this season - two of the six sides higher than Manly on the ladder to begin the weekend.
Prior to the Tigers loss, Seibold said he was "very confident" the Sea Eagles would play finals football this season and that faith was not shaken on Thursday night.
"I'm confident in our team, of course I am," he said.
"I'm not sure what the ladder looks like after tonight but we've been reasonably consistent over the last little period of time.
"It's disappointing but it's not the end of the world, right? We're fighting in this competition and we'll go again.
"It's going to be a disappointing 24 hours but then we need to wash it after that."
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