Newbury has one point in one game. The others have yet to score.
"Guys are squeezing their sticks," Berube said.
"He's fine, he's healthy," Berube said after the Flyers' inartistic 2-1 win over visiting Florida on Tuesday night. "I think G's trying a little bit too hard. He gives everything he's got out there and sometimes it's too much. You try too hard and you can't accomplish the things you want to accomplish."
Playing on a line with Jaromir Jagr two seasons ago, Giroux (93 points) and Hartnell (37 goals) had career seasons.
Minus Jagr, Giroux had 48 points in 48 games last season, while Hartnell had eight goals and 12 points in an injury-plagued year.
"I'm not confident right now," said Giroux, adding that "you always have a stretch like that during the season."
Berube, in his first game as head coach, moved Wayne Simmonds onto Giroux's line Tuesday. He will give the trio a chance to develop some chemistry.
"It's been a struggle, especially for our line. We have to get things figured out," Hartnell said after Wednesday's practice in Voorhees. He credited goalie Steve Mason for the Flyers' escaping with Tuesday's win, "but we have to score more than two goals a game to have any success this season."
Hartnell said that when he's having success, "it's pretty simple. I score my goals right in front of the goalie, right in his face. Get tips and rebounds. Go to the net with the stick on the ice and good things happen. I've obviously gotten away from that a little bit. I talked about it yesterday with [Simmonds] . . . Just throw pucks at the net and me or him will be there.
"We just have to give G some space to make plays like he can," Hartnell added.
The Flyers had their first full practice under Berube on Wednesday. They are learning his defensive system, one that uses a three-man forecheck to help prevent odd-man rushes. Berube saw progress in the forecheck against Florida, but thought his team allowed too many quality scoring opportunities.
"We've got to have more awareness," Berube said. "We puck-watch too much."