Serena Williams is ready for her comeback after more than a year out and Roger Federer is aiming to take back the world number one spot.
Williams hasn't played a WTA tournament since winning last year's Australian Open and skipped this year's opening grand slam due to concerns about her fitness four months after giving birth to her first child.
Federer meanwhile will bid to replace Rafael Nadal as men's world number one when he competes in Rotterdam next week.
Williams will be "ready to go" when she returns to action this week in the United States' Fed Cup first round tie against the Netherlands, captain Kathy Rinaldi said on Wednesday.
Rinaldi said she expects Williams, who was named in the US squad that will compete on an indoor hard court in Asheville, North Carolina, to make a smooth transition in her return to competitive tennis.
"Serena's just coming back. She played an exhibition in (December) and it's incredible," Rinaldi said.
"It's a quick turnaround after having her first child. She's very professional and she has a lot of pride for playing for her country. She'll be ready to go."
Williams, 36, has played once since winning an Open-era record 23rd grand slam singles title in Melbourne last year, losing to French Open champion Jelena Ostapenko in an exhibition match in Abu Dhabi last December.
She heads a team made up of older sister Venus, world number 17 CoCo Vandeweghe and world number 62 Lauren Davis. The United States beat Belarus last year for a record-extending 18th Fed Cup title, their first in 17 years.
The Netherlands squad is comprised of world number 108 Richel Hogenkamp, Arantxa Rus (124), Lesley Kerkhove (165) and Demi Schuurs, who is ranked 32nd in doubles. Play takes place on Saturday and Sunday.
Federer, also 36, won his sixth Australian Open title and 20th grand slam in January and reaching the semi-finals of the Rotterdam Open in Holland would return him to top spot in the ATP rankings.
He would also surpass Andre Agassi as the oldest ever world number one - the American was 33 when his sixth stint at the summit of men's tennis ended in September 2003.
Federer, who won the event in 2005 and 2012, told his official website: "The tournament is special for me.
"I remember playing for the first time in 1999 as it was one of the first events where I got the chance to play at the highest level. It feels good to join in the celebrations of the 45th edition."