Scotland have "enough quality, determination and experience" to reach the 2018 World Cup finals in Russia, according to Stuart McCall.
The outgoing Scotland assistant coach, appointed Bradford City manager for a second time, is stepping down from Gordon Strachan's staff.
Scotland have failed to qualify for a major finals since featuring in the 1998 World Cup in France.
"It has been an honour and a privilege to serve my country," added McCall.
McCall's contract with the League One outfit sees him step down from his Scotland duties but the 52-year-old remains confident of the national side's future under Strachan.
In a statement on the Scottish FA website, McCall said: "Firstly, I would like to thank Gordon, [assistant] Mark [McGhee], the playing staff and the backroom team for making my time as assistant national coach so enjoyable.
'I'll miss working with the players'
"While I am as disappointed as any fan that we did not qualify for the Euros I remain convinced that we have enough quality, determination and experience to reach the World Cup finals in Russia in 2018.
"It has been an honour and a privilege to serve my country and I would like to thank the Scottish FA for that opportunity, as well as my previous clubs, Motherwell and Rangers, for enabling me to assist Gordon and Mark.
"I've never hidden my desire to return to club management and I am delighted to be back at Bradford, a club that is dear to my heart.
"The programme of fixtures means I can no longer continue to work with Scotland but I spoke to Gordon when the opportunity arose and, as you would expect, he was terrific, fully understood the situation and wished me the best of luck.
"I will miss working with the players and staff and will join the thousands of fans supporting the team when the qualifiers begin in September."
Strachan believes McCall will do "an excellent job" as he returns to club management in England.
"He was a really valuable member of the team and will be missed: not only was he an excellent coach, but he was popular with the squad and backroom staff and had a passion and infectious enthusiasm about playing his part for his country," the Scotland manager added.
Scotland 'have lost ability to intimidate' - Boyd
Former Celtic and Scotland defender Tom Boyd, a former international team-mate of McCall's, questioned whether the current side have the requisite 'grit' to succeed.
"The determination thing seems to be getting taken out of Scottish football," Boyd told Radio Scotland.
"We used to have that grit and ability of intimidating opponents. That seems to have been lost a wee bit and the nature of the game has changed.
"We have the quality, we've seen that in the earlier part of the previous campaign [the Euro 2016 qualifiers].
"The thing that may help is blooding some youngsters. Yes, we have the experience but I would like to see some of the youngsters getting a try a bit earlier in the campaign.
"We've got to make sure we qualify [for the 2018 World Cup]. It's been a long time since we got to one."