The 33-year-old signed a two-year deal with the Capital club last weekend following his release from Saudi Arabian side Al Ahly, joining Socceroos team mate Jamie Maclaren, and Arnold reckons the former Melbourne Victory and Sydney utility man can flourish in Edinburgh after landing his dream move to Europe.
Arnold told ESPN: “When I spoke to Mark two weeks ago, he was a bit on edge and down - you could feel it down the phone line.
“But the other night, he rang me and he was so joyful and happy. For him, mentally, after he finishes playing, it’s a big thing for him.
“He’s done everything in the A-League, been to four World Cups... the one scar he needed to scratch was to go overseas and play in a European league.”
• READ MORE - Hibs snap up midfielder Mark Milligan on two-year deal
Linked with Arsenal, Blackburn Rovers, Manchester City, RC Lens, Metz, Werder Bremen and Porto at various points during his career, Milligan has sampled football in his homeland as well as in Japan, China, Saudi Arabia and the United Arab Emirates but never managed to secure a move to Europe.
With his club future now sorted out, Arnold - a former striker who played in Europe with Roda JC, Liege and NAC Breda during his 21-year career - is hopeful that Milligan might rethink his decision to hang up his international boots.
The 71-cap Socceroo, who played in all three of his country’s matches in Russia, hinted that he might retire from the national team after the World Cup, but Arnold hasn’t given up hope of including Milligan in his squad for the Asian Cup in January, and feels playing in Scotland’s top flight under Neil Lennon may encourage the Sydney-born player to rethink his decision.
“Mark’s going to get to play against Celtic, and Rangers - big clubs - and Hibs is a great club as well, Neil Lennon is probably the perfect manager for them,” Arnold explained.
“He sounds like a manager who cares for the person.
“Mark just wanted to sort out his club future. There’ll be another conversation between us about what it looks like going forward [in terms of the national team] but it’s one step at a time,” he added.