Yeo will head for further examination over the weekend after failing to finish Friday's 28-12 loss to the Warriors with a suspected pectoral injury.
It would be a devastating blow if Yeo, who was set to captain Australia at this year's World Cup, misses their run towards September which starts with next Thursday's battle with the Roosters at CommBank Stadium.
The two teams are level on 36 points after Leniu's side edged past Canterbury 20-18.
But the three-time Penrith premiership winner is expecting his former club to come out all guns blazing even if they are deprived of Yeo for the back end of the year.
"It's a massive loss, he is sort of the heartbeat of their team and knowing Penrith, they are a world-class team and there'll be that next-man up mentality," Leniu said.
"They've been doing it for the last couple of years and they've filled those voids when it comes around.
"He's their captain and when a lot of experience goes off the field you notice it.
"But the Penrith Panthers are a well oiled machine and no doubt they'll still be pushing for the premiership at the end of the year.
"If you get that tap on the shoulder you've got a duty to perform and wear that jersey with pride and that's been the forefront of the Penrith Panthers."
The injury to Yeo and the loss in Auckland has firmly brought Penrith back to the pack in the battle for the minor premiership.
The Panthers only hold on to top spot as a result of their for and against but will be overtaken by the Roosters if Trent Robinson's men can claim an eighth straight win.
"They've been the benchmark for the whole competition the last few years and this (a win) would put us in good stead," Leniu said.
"No doubt they'll be our biggest competition for the year and truly see what this team is about.
"I've got a lot of confidence in this team and the boys inside our four walls… we know we can play s**t footy and still win games.
"Whenever we get that good side of the coin and we're playing good footy we know we can beat anyone."
