The 26-year old attacking midfielder travelled to Switzerland on Monday night and is expected to sign a deal with Sion this week after he was given permission by the Reds to leave.
"Dario has a great opportunity to play in Europe again which is something he was keen to do," Adelaide's football operations manager Michael Petrillo said yesterday.
"After receiving a transfer request from FC Sion I can confirm that both clubs have agreed to terms for Dario's transfer and at this stage it's likely he will leave for Switzerland tonight.
"Dario was Adelaide United's Club Champion last season, he has played some great games for us and we thank him for his contribution to the club over the last two years and wish him well for the future."
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