The Wanderers are reeling from a poor season in which they finished second bottom of the A-League and failed to survive the group stage of the AFC Champions League.
Less than seven months since the Wanderers caused a major upset by winning the Asian title after beating Saudi Arabia's Al Hilal, the young club was faced with the possibility of losing its driving force Popovic.
But his decision to stay on was probably the Wanderers' biggest signing, Spiranovic claimed.
"Poppa has done a remarkable job in a short time and having him stay on at the club is a great coup without doubt," Spiranovic said.
"We proved our quality and showed what we can do in our last group game with Guangzhou Evergrande, which is Asia's biggest club with the biggest finances.
"We'll be back next season, no doubt."
Spiranovic, who is now an established international after playing in the FIFA World Cup in Brazil and being a member of the Socceroos' AFC Asian Cup-winning team, said the double commitment of playing in the A-League and in Asia was the main reason behind the Wanderers' dramatic dip in form.
"Our schedule was our biggest problem," Spiranovic said. "It was physically and mentally very challenging.
"We played Champions League a year ago and then won the quarter-finals and semi-finals in our pre-season.
"We won an ACL final and went to the Club World Cup while playing in the A-League and then played in the Champions League again, all this while having a 23-man roster and playing against teams with 10-20 times our budget.
"We averaged about nine or 10 injuries to our squad for the last few months of our season.
"We had eight consecutive matches in around February and March where we lost a player to injury in the first half. These are not excuses, they are facts and no other A-League club has had to face them but we will be stronger for it."
After releasing a host of players including veteran goalkeeper Ante Covic and attacking trio Tomi Juric, Kerem Bulut and Nikita Rukavytsya at season's end, Popovic will look to add some quality to the playing group with Perth Glory duo Danny Vukovic and Scott Jamieson touted as targets.
Support staff changes have seen Ian Crook swap assistant coach duties for a role as technical director of the Wanderers’ Elite Academy structure with Zeljko Kalac to cross the divide from Sydney FC to link up as goalkeeping coach.
Spiranovic missed the Socceroos' last two matches against Germany and FYR Macedonia due to a hamstring injury he suffered in the Wanderers' ACL match at FC Seoul.
He is expected to be picked in Ange Postecoglou's squad for the first World Cup qualifier against Kyrgystan in Bishkek on 17 June (AEST).
Spiranovic, who at 26 is a seasoned campaigner having played at the top level in Germany and Japan, will put his club's poor form behind him as he bids to play in his second World Cup in Russia in three years.
"You just cannot let adversity affect your game," he said. "I proved during Asian Cup time that I can handle the things I'm in control of.
"I'm the type of bloke who does not look back but welcomes the next challenge.
"This comes with age and experience.
"I've been a professional footballer for quite a while now and you learn how to deal with the ups and downs, same as you do in life in general.
"Regarding the World Cup campaign we will prepare for the games as if we are facing the world champions.
"That is how Ange approaches things and the team will be ready for our first game in June.
"We are getting better with every game especially in defence.
"In Brazil we played against world class opposition and we got punished for every mistake."
