Hertl is day-to-day and will miss a third straight game because of a lower-body injury, Sharks coach Peter DeBoer said.
With a win, the Penguins would clinch their fourth championship, first since 2009. Coach Mike Sullivan said he wants his players to embrace the moment but contain their excitement.
"I think our players have this game in perspective," he said. "We're at our best when we play with emotion, play with energy. But it certainly has to be controlled emotion."
The Sharks need a victory to prolong the series. Game 6, if needed, would be at SAP Center in San Jose on Sunday.
Helping make that possible would be playing with the lead for the first time in the series. Their victory in Game 3 came in overtime.
"We've talked about scoring first, and obviously if we don't tonight we can't just back the bus up and head home," DeBoer said. "But we want to play with a lead. We want to put them in a position where they're playing from behind. We haven't done that yet."
Hertl's absence could make that more difficult.
Before the injury he arguably was San Jose's most effective player in the first two games against Pittsburgh. He scored 3:02 into the second period of Game 1 to extend his points streak to three games. That streak ended in Game 2 when he had two shots on goal and hit the goal post three times.
In his absence, forward Melker Karlsson has moved to first-line left wing alongside center Joe Thornton and right wing Joe Pavelski.
Pavelski has zero points in the series after he had 13 goals and 22 points through the first three rounds. Karlsson scored for the Sharks in their 3-1 loss in Game 4 on Monday.
When facing elimination in Game 7 of the Western Conference Second Round against the Nashville Predators, the Sharks put together one of their better playoff efforts in a 5-0 win. Thornton said he would like to see that replicated Thursday.
"I think we're really good when we attack," Thornton said. "I think tonight we need to attack and play aggressive. Usually when we do that we have good results."
Penguins forward Nick Bonino did not practice during an optional morning skate Thursday. He also did not practice Wednesday because of a maintenance day. Sullivan said Thursday he has "no concern" regarding Bonino's availability Thursday.
Bonino is tied for second on the Penguins in the playoffs with 17 points while centering the "HBK Line" with left wing Carl Hagelin and right wing Phil Kessel. He also leads the Penguins with 18 blocked shots in the Final.
"[Bonino] is an extremely good player when it comes to blocking shots and his defensive awareness," Hagelin said. "He's fun playing with because he wins battles and he makes plays, so a lot of big blocks from that guy."
Here are the projected lineups:
SHARKS
Melker Karlsson - Joe Thornton - Joe Pavelski
Patrick Marleau - Logan Couture - Joonas Donskoi
Matt Nieto - Chris Tierney - Joel Ward
Dainius Zubrus - Nick Spaling -Tommy Wingels
Paul Martin - Brent Burns
Marc-Edouard Vlasic - Justin Braun
Brenden Dillon - Roman Polak
Martin Jones
James Reimer
Injured: Tomas Hertl (lower body)
Scratched: Micheal Haley, Dylan DeMelo
PENGUINS
Conor Sheary - Sidney Crosby - Patric Hornqvist
Chris Kunitz - Evgeni Malkin - Bryan Rust
Carl Hagelin - Nick Bonino - Phil Kessel
Tom Kuhnhackl - Matt Cullen - Eric Fehr
Brian Dumoulin - Kris Letang
Olli Maatta - Ben Lovejoy
Ian Cole - Justin Schultz
Matt Murray
Marc-Andre Fleury
Injured: Kevin Porter (ankle surgery), Scott Wilson (lower body), Trevor Daley (ankle)
Scratched: Jeff Zatkoff, Derrick Pouliot, Oskar Sundqvist, Beau Bennett, Kael Mouillierat, Jean-Sebastien Dea, Daniel Sprong, Tim Erixon, Josh Archibald, Dominik Simon, Steve Oleksy, Tristan Jarry
Status report:Crosby, Malkin, Kessel and Letang also sat out Pittsburgh's optional morning skate. … Zubrus is expected to play in a third consecutive game with Hertl out.
Who's hot:Kessel has at least one point in 15 of 22 playoff games. He leads Pittsburgh with 10 goals and 21 points. … Before being held without a point in Game 4, Ward had at least one point in four of his previous five games. He has one goal and one assist in the Final.
