The USA international had arrived in England hoping to find a new employer following his release by Philadelphia Union.
Blackpool boss Barry Ferguson was prepared to offer him a window in which to impress, with Adu spending three weeks with the Seasiders.
He figured in two behind-closed-doors fixtures during that time, but has not done enough to earn a permanent deal.
The door at Bloomfield Road has not been completely closed on Adu, though, with the 24-year-old having been granted permission to continue working on his fitness at the Championship club.
Ferguson told the Blackpool Gazette: "There is nothing happened with Freddy.
"He's come in and worked hard with us. He is a great lad but I'm more than happy with what I've got. I have a strong squad."