The 32-year-old, who won 102 caps for the Lionesses, left Juventus in December after nearly 18 months with the Serie A champions and had been tipped to return to the Women's Super League.
"Thank you football for everything you've given and taught me," said Aluko on Twitter. "Thanks for the full circle moments and crazy unexpected journey."
Aluko, who played for Birmingham, Charlton and Chelsea in England, as well as having a brief spell in Northern America, was part of the Great Britain team at the London 2012 Olympics.
She scored 33 goals for England and her last international appearance came in 2016 but she was subsequently involved in a discrimination case against former boss Mark Sampson in 2017.
Aluko accused Sampson of making racist remarks and the Football Association apologised to her in October 2017 - three years after the comments were alleged to have been made.
Writing in The Players' Tribune, Aluko wrote a letter thanking football for the "crazy, unbelievable journey" it has taken her on during her career, which began in 2001.
"When we met...I was just a girl from a council estate in Birmingham. I could never have imagined the crazy, unbelievable journey you would take me on," she wrote.
"You have given me the dream of playing in the US, the pride of representing England, the thrill of winning titles with Chelsea, the adventure of playing for Juventus in Italy.
"Whenever I have faced obstacles, you have shattered them. Whenever I have had great expectations, you have exceeded them."
