A three-game losing streak would increase pressure on a Sharks side tipped as pre-season premiership fancies but Fitzgibbon said round six was too early to start worrying.
The 10th-placed Sharks have been contending with illness in camp in recent weeks as well as injuries to Kayal Iro, Sifa Talakai, Braden Hamlin-Uele and Tom Hazelton, and only lost to Canberra in round five when Seb Kris crossed for a late match-winner.
The previous defeat came against Canterbury, the NRL's only unbeaten side through five rounds.
"There's no concerns from us, that's not a word we're using at this stage of the year at all," Fitzgibbon told AAP.
"The effort, the attitude is right. We're working hard for each other.
"We've got to fix a few areas up but there's a long, long way to go. We've got a lot of improvement in us."
Second halves appear a key area for improvement.
Between rounds three and five, the Sharks scored the fewest second-half points (9) of any team that played three games.
They managed only one try in that time, a league low equalled only by Newcastle, who had the bye in round four.
Fitzgibbon said the quality of his side's opponents had played a role in the dearth of second-half points.
"Sometimes it's the timing of how and when you play against a team, our situation versus theirs," he said.
"There's obviously some work-ons there, we'd like to have performed better there.
"We're under no illusions about the fact we have to improve."
Manly have spent the entire week in Perth following a hefty 48-24 loss to Melbourne last Sunday, spending part of the trip training at the Western Force's facilities.
Winger Jason Saab has been ruled out with an ankle injury, but Tommy Talau is listed to finally make his return from a hamstring tear in his place.
"It was a disappointing performance against Melbourne," said coach Anthony Seibold.
"We reviewed the game Monday evening and from Tuesday morning it's been full focus on the Sharks."
Manly second-rower Haumole Olakau'atu lines up for his 100th NRL game, having debuted against the Sharks in 2019.
"I love his journey, I love what he stands for as a bloke on and off the field," said Seibold.
"Earlier this year we put him in the leadership group because he's a genuine leader."
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