Giorgio Chiellini bowed out of international football and warned a "difficult period" awaited Italy as Roberto Mancini bids to get the Azzurri back on track.
The joy of winning last year's delayed Euro 2020 tournament has been replaced by rapid deflation after Italy failed to qualify for the World Cup.
Having also missed out on the Russia 2018 finals, falling short of a place at Qatar 2022 represented crushing disappointment for the four-time winners.
Chiellini, the 37-year-old defensive titan who is leaving Juventus and expected to join Los Angeles FC, has called time on his Italy career.
He played the first half on Wednesday in a 3-0 defeat to Argentina at Wembley, in a match tagged as the Finalissima, a clash of the champions of Europe and South America.
"We were hoping to win the match and the trophy," Chiellini told Italian broadcaster RAI. "We knew it would be tough, but the defeat does not cancel what has gone before.
"Now I expect a difficult period. We need everyone to support this group."
Chiellini lasted just 45 minutes in his farewell game, with Italy 2-0 up by the time he departed.
This was the first staging of the CONMEBOL/UEFA 'Cup of Champions' since 1993. Lautaro Martinez, Angel Di Maria and Paulo Dybala got the goals as Lionel Messi pulled the strings
It was a sorry way for Chiellini to go out, and he said: "It's a shame because in the first half we made a lot of mistakes and we ruined the match by ourselves."
Turning his attention to Argentina, he added: "Above all, at this moment they are too strong, they have confidence and they are a team. They look like us a year ago."
Italy, without Chiellini, will switch their focus to the Nations League. They face Germany on Saturday and again on June 14 – matches against Hungary and England are sandwiched in between.
Writing on his Instagram page, Chiellini reflected on the end of a 117-cap career.
He wrote: "Thanks to everyone, it's been a beautiful journey."