Russia coach Vyacheslav Bykov will benefit from the extra firepower after the Penguins were eliminated from the Stanley Cup playoffs by the Montreal Canadiens.
Teams at worlds are allowed to have 20 skaters and three goalies in the first round and can add two more players for the second round.
The two-time Olympian Malkin will play in his fourth worlds and was a leading figure in Pittsburgh's 2009 Stanley Cup title run, earning the playoffs' most valuable player award.
"It's my national team and they called me. If my team needs me and I can go, I'm not going to say no," Malkin said Friday in Pittsburgh.
Gonchar, a four-time Olympian, had 13 goals and 49 assists in 75 games this season. He was planning to leave later Friday, while Malkin expects to travel on Saturday.
"I was disappointed with this season. I wasn't satisfied," Gonchar said. "And I've never won a world championship."
Losing in the Olympics -- the Russians were beaten 7-3 by eventual gold medalist Canada in the quarterfinals -- is another reason why Malkin and Gonchar wanted to keep playing.
"It was emotional and I was very mad," Malkin said of losing in Vancouver. "If we win now, we'll play better and it would be good. I think we can win, we've got a good team."
Other recent big-game additions to the rosters included Germany bringing in Christian Ehrhoff of the Vancouver Canucks; Finland adding 22-year-old forward Oskar Osala of the Carolina Hurricanes; world juniors MVP Jordan Eberle joining Canada; and Mikael Backlund of the Calgary Flames helping Sweden.
While many teams were adding players, surprise team Norway will lose two due to suspensions.
The worlds' disciplinary panel on Friday suspended Norway forward Martin Laumann Ylven for two games following a first-period blow to the head of France's Antonin Manavian, who did not return to the game due to concussion.
Norwegian goalie Pat Grotnes was banned for one game after shoving France's Yorick Treille and then hitting him on the head with his stick in the third period of the same game.