World No.77 Kokkinakis confirmed his absence from the Brisbane tournament, which starts on Sunday, on social media.
"Sad to miss the Brisbane International this year," Kokkinakis wrote.
"Dealing with a small hip issue that needs some more time, but hopefully back for the rest of the summer."
Sad to miss — Thanasi Kokkinakis (@TKokkinakis) @BrisbaneTennis this year. Dealing with a small hip issue that needs some more time, but hopefully back for the rest of the summer ✌�December 26, 2024
If Kokkinakis recovers, his first tournament of the Australian summer would be the Adelaide International from January 6.
The 28-year-old South Australian won his home tournament in 2022, claiming his first ATP title.
Tomljanovic is hopeful of recovering from a left knee injury in time for the first grand slam of the year but the world No.109 will miss the Brisbane International and Hobart International in the lead-up.
The Australian Open begins in Melbourne on January 12.
"I'm so disappointed to withdraw from the Brisbane International but I wanted to be 100 per cent ready to compete, which I am not," Tomljanovic said on Instagram.
"I'll continue my prep and see you all at the Australian Open."
Ajla Tomljanovic grimaces during a 2024 Australian Open match in Melbourne. (James Ross/AAP PHOTOS)
Tomljanovic missed this year's Australian Open, French Open and Wimbledon due to her knee injury.
The 31-year-old's last appearance on the WTA Tour was at the Merida Open in Mexico in October.
Kokkinakis's last event was the UTS Grand Final in London in early December.
Australia's Maddison Inglis won her first round qualifier at the Brisbane International. (Darren England/AAP PHOTOS)
Meanwhile, the first round of women's singles qualifiers for the main draw in the Brisbane International were held on Friday but it was not a good day overall for the Australians.
Of the eight Australians taking part only Priscilla Hon and Maddison Inglis won through to the second round of qualifiers to be played on Saturday.
Hon had a 7-6 7-6 win over Britain's Harriet Dart while Inglis overpowered Belgium's Ysaline Bonventure 6-2 6-4.
World No.167 Hon, 26, will now play China's Guo Hanyu while 26-year-old Inglis, ranked 156, takes on Ukraine's Anastasiia Sobolieva.
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