Their long-time Tour de France and race partnership ended when the 62-year-old Englishman died in his sleep of heart failure in December.
"I've evaluated every day in my life since," Liggett told the Australian Associated Press.
"The last thing I want to do is crack up. It's going to be very difficult at the Tour Down Under."
The duo called the Tour de France for 33 years together. After Sherwen's death, 75-year-old Liggett doubted whether he would continue the work.
"Because I spoke about it almost non-stop from the moment I was told, the grief flew over my head," Liggett said. "I don't think it's hit me yet."
For the WorldTour stage race in Adelaide, Australia, Liggett will commentate with former Australian sprinter Robbie McEwen.
"Robbie is a natural on television, a total natural," he continued. "He's a friend. I'm not at all worried about working with Robbie."
Liggett used to grab Sherwen's knee to signal he would start commentating. With McEwen, the tradition will likely continue.
"I'm just a little bit afraid I might grab his knee. I will let you know [the reaction], I hope Robbie understands.
"It's no good, it will slip," Liggett added when asked if he thinks he might accidentally refer to McEwen as Sherwen and say "Paul".
"I think that's a sign of friendship."
The men's Tour Down Under starts with a criterium on January 13. The stage race begins two days later.
Liggett explained that no decision has been made on who will work beside him at the 2019 Tour de France.
Gregor Brown is an experienced cycling journalist, based in Florence, Italy. He has covered races all over the world for over a decade - following the Giro, Tour de France, and every major race since 2006. His love of cycling began with freestyle and BMX, before the 1998 Tour de France led him to a deep appreciation of the road racing season.
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