United, who will announce the signing of defender Nick Ansell today, recently indicated they had four players about to join their stocks.
Blackwood will become the second of those four, with former captain Isaias also on their hit list.
The utility returns to Adelaide after one season playing in England for Oldham Athletic.
He was lured there by former Socceroo Harry Kewell, who was appointed manager at Greater Manchester side for the 2020/21 season.
Unfortunately for Blackwood, Kewell was sacked by Oldham in March and he fell out of favour.
In all, the 24 year-old made 14 appearances for Athletic, scoring three times in all competitions.
Blackwood’s first stint at Adelaide United yielded 16 goals over three seasons.
United is expected to make the announcement early next week.
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