Cahill returned to his home in the United States to be with his family with his Milwall contract coming to an end.
The 38-year-old's playing future is once again unclear as he banks on previous performances in the green and gold to help him play at his fourth FIFA World Cup for Australia.
Cahill made headlines in January when he signed with Millwall for the second time in his career, after leaving A-League club Melbourne City in search of more playing time.
However, Cahill's fairytale return to his first professional club failed to pan out, with the forward having minimal impact on the Lion's unsuccessful push for Premier League promotion.
In 10 appearances, all from the substitutes bench, Cahill failed to score and played only a total of 63 minutes during his five month stay at the South London club.
He also received four yellow cards and was suspended for the final three games of the season.
Including his six appearances for Melbourne City, Cahill has played only 157 minutes of club football this season.
"Time flies when your (sic) having fun. Massive thank you to everyone in the club, the fans and most importantly the players," Cahill wrote in a post on his Twitter account.
"A lot to be proud of this season and I have had the best time being back home where my career began. Blessed to have had this opportunity."
Cahill was included in Bert van Marwijk’s initial 32 player squad for the World Cup but could still be a high-profile omission when the final squad is announced next month.
