Tomic, 19, has been asked to step up as the No.1 player for his country in the tie against lowly South Korea starting in Brisbane on Friday.
World No.36 Tomic on Thursday was drawn to meet unheralded Min-Hyeok Cho, a player who does not have an official ranking with the ATP, in the opening singles clash.
World No.18 Australia's Chris Guccione and Marinko Matosevic have been pencilled in for Saturday's doubles clash.
Rafter backed Tomic to stand tall in the Asia-Oceania group second round tie with Hewitt unavailable until June due to a foot injury.
"We are playing a team that is lowly-ranked," Rafter said.
"I see that as not a lot of pressure on Bernard at all.
"If it was a tougher tie I would think he would have a bit more of a burden but he's someone who thrives in adversity. He loves the pressure."
Tomic admitted he had no idea about his opponent who has a career-high ranking of 666.
"That's where it can be tough," Tomic said.
"I am much better-ranked but that doesn't mean anything.
"In Davis Cup players play much more freely and relaxed, hopefully I get up tomorrow.
"Whatever they throw at us we have to be ready."
The tie is a stepping stone as Australia look to break back into the elite World Group for the first time since 2007.