Devils coach Pete Deboer confirmed following his team's optional skate that Zajac did not feel good enough to play.
"Travis is day-to-day and a decision has not been made on whether or not he will join the team in Minnesota [to face the Wild on Sunday]," DeBoer said.
Zajac appeared to sustain an ankle injury during practice Friday. According to reports, the veteran center tripped and fell during the early stages of practice and was replaced by Josefson.
Zajac told reporters afterward he caught a rut in the ice and that his falling over was laughable.
Zajac, who missed all but 15 regular-season games in 2011-12 after tearing his left Achilles tendon that summer, has one goal, four points and a minus-5 rating in 12 games for the Devils this season. Since sustaining his Achilles injury, Zajac has 10 goals and 30 points in 75 regular-season games.
"I'm with two great players, so I'll try to keep it simple and solid and play good defensively," Josefson said. "It might take a period to get that tempo going again, but I should be fine."
DeBoer is hopeful Josefson can have an impact despite missing the past four games as a healthy scratch.
"Anytime a young guy gets in, we want him to make it so we can't take him out of the lineup," DeBoer said. "That doesn't mean he has to score, but he's got to bring energy and be responsible and make us trust putting him on the ice. I think he's capable of doing it and seizing the opportunity."
Goalie Cory Schneider remains on injured reserve, leaving Keith Kincaid to back up Martin Brodeur. Schneider has missed the past two games while dealing with a lower-body injury. He said he felt fine at practice Saturday.
"I'm feeling good; this was the longest and hardest I've been on the ice so far," Schneider said. "We did a lot of in-tight stuff."
The game against the Flyers opens the Devils' third of 22 sets of back-to-back games. Schneider, who sustained his injury Oct. 24 in a loss to the Vancouver Canucks, could get the start Sunday when the Devils travel to Xcel Energy Center to play the Minnesota Wild. In Schneider's absence, Keith Kinkaid has served as backup to Brodeur the past two games.
Brodeur will look to notch his third straight victory. He has allowed four goals and has had several timely saves in wins against the Boston Bruins and Tampa Bay Lightning on this current run. The 41-year-old strung together three consecutive wins on three occasions in 2012-13, the final streak coming in late March when he yielded four goals in victories against the Washington Capitals, Carolina Hurricanes and Florida Panthers.
"Just for the team to win a couple of games in a row is great," Schneider said. "To finally get rewarded for our hard work is good. Marty played really well and has made some big saves, so it's great to see the team win. Whether it's me or him [in goal], we'll take it."
Dainius Zubrus, who didn't take part in the optional skate Saturday along with Zajac, Patrik Elias, Michael Ryder, Steve Bernier, Andy Greene and Marek Zidlicky, is expected to appear in his 1,100th game. Ironically, Zubrus' father, Gintas, also celebrates his 60th birthday.
Here is the projected lineup for the Devils: