"The situation is that for the next three to four months, I don't want to take the coach... I go with the flow and I see how it works," French Open champion Halep told the WTA website.
"He took the decision because of family and family always comes first. I wasn't disappointed or upset, I fully understood. We have a very good relationship."
Cahill has a long track record as a coach, helping compatriot Lleyton Hewitt reach number one in the rankings as well as reviving the career of American Andre Agassi.
"It's tough... but I feel confident I can do my own things on court. I'm more responsible now on everything that I have to do. Maybe it's a good thing, I will see," Halep added.
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Meanwhile, Halep said she was pain-free following a back injury that cut short her 2018 season, but believes this week would be the real test of her fitness.
Halep won her maiden Grand Slam at Roland Garros last year but was diagnosed with a herniated disk in October which ruled her out of the season-ending WTA Finals.
The Romanian retained her top ranking for a second straight year despite missing the Singapore tournament and said she was raring to go after a spell during recovery where she did not pick up a racquet.
"The back was good for the off-season. I didn't have pain and I trained 100 percent, I played some sets, some matches," Halep said.
"No pain, no stress, but you never know until the official matches, so I'm waiting for this week to see how I feel... I have no pressure, but I'm motivated to see how good I can be this year.
"Six weeks I did nothing, just in the gym to do exercises every day for one hour. No tennis. It was a long time... it's going to be a tough start because I have almost three months without official matches."
Top seed Halep, who has a bye into the Sydney second round, will face either Jelena Ostapenko or local hope Ashleigh Barty.
(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Christian Radnedge)
