Federer, who played Britain's Andy Murray in the Australian Open men's final on Sunday, will begin his 268th week as No. 1 and match Jimmy Connors, currently in third place, for total number of weeks as world No. 1.
Pete Sampras leads the career list with 286 weeks at No. 1, followed by Ivan Lendl with 270.
If Murray beats Federer at Melbourne Park, he could move to No. 2. Otherwise, projections have Novak Djokovic taking over No. 2, Murray third and injured Rafael Nadal dropping to No. 4.
It marks the first time that Nadal will drop out of the world's top three since his debut there in June 2005.
Nadal has been cleared of a recurrence of the knee tendinitis that sidelined him for nine weeks last year. A small muscle tear sustained at the Australian Open, where he lost in the quarterfinals to Murray, will keep him out for the next month.
"It is not important for me, the ranking issue and losing a few spots _ that's normal when you are not able to compete," Nadal said.
There will be movement on the women's side, with Li Na becoming the first Chinese player ever to enter the top 10 when she reaches a career high No. 10 following her semifinal run here.
Justine Henin, who was unranked and playing on a wild-card entry at her first major in two years, still needs to play another tournament before she gets an official ranking.
Williams, who beat Henin in Saturday's Australian Open final, has extended her current stretch at No. 1 to 15 weeks. Projections provided by the WTA show Williams will begin her 88th career week as the top-ranked player.
Dinara Safina is projected to be No. 2, followed by U.S. Open finalist Caroline Wozniacki at a career-high No. 3, French Open champion Svetlana Kuznetsova at No. 4 and Australian Open quarterfinalist Venus Williams at No. 5.
Projections also show Victoria Azarenka, who lost to Serena Williams in the quarterfinals, to be No. 6, followed by Elena Dementieva at 7. It's the first time that Olympic gold medalist Dementieva, who lost to Henin in the second round here, has dropped out of the top 5 since September, 2008.
Jelena Jankovic is projected to be No. 8, Aznieszka Radwanska 9 and Li at 10.
Li said after her quarterfinal win over Venus Williams that her goal was the top 10, but she may have to revise her expectations higher.
"So exciting, maybe I will have a beer tonight," said Li, who lost in the semifinals to Serena Williams. "My goal this year was top 10, but it's only January, and it's come quickly."
Henin, who quit in May 2008 while holding the No. 1 ranking, has to play three tournaments before she re-enters the rankings.
The 27-year-old Belgian lost the Brisbane International final to U.S. Open champion Kim Clijsters in Henin's first tournament back. After her finals appearance at Melbourne, another good showing at her next tournament, which is expected to be in March at Indian Wells, California, could see Henin return in the top 50.
Clijsters returned to the rankings at No. 19 ahead of the fourth and last event of her comeback season at Luxembourg, where she was ousted in the second round.