Roberto Mancini was unable to secure Champions League football. Alexander Demianchuk/TASS via Getty Images

For the third season in a row the richest club in Russia, Zenit St Petersburg, won't take part in the Champions League. Once again they failed to qualify after a 1-0 defeat to champions Lokomotiv Moscow at the weekend left them trailing in fifth place -- five points off third with one game to go.

It is an enormous surprise in the country as Zenit were considered clear favourites to claim the title after hiring Roberto Mancini and making heavy investments in the summer.

This was supposed to be Zenit's year. CSKA Moscow and tiny Rostov finished ahead of them in 2015-16, as Andre Villas-Boas announced his departure long before the season had ended; Mircea Lucescu's appointment in 2016-17 proved to be disastrous, as bitter rivals Spartak Moscow were crowned champions for the first time since 2001 and CSKA finished a point ahead of Zenit in the final table to deny them a spot in Europe.

But, after a summer of revolution, Zenit had high hopes. In previous seasons only the Russian champions qualified directly for the Champions League, while the runners-up had to go through the qualifiers. However, ahead of 2017-18, the new UEFA format significantly improved their chances, giving Russia two automatic places in the group stages, with the club that finishes in third place admitted into the qualifying round.

Since 2009, Zenit had always finished in the top three, so getting back into the Champions League was almost taken for granted.

Former Manchester City and Inter Milan boss Mancini officially replaced Lucescu at the beginning of June, signing a three-year contract with an option for additional two seasons, and changes were swift.

Legendary captain Danny was forced to leave the club just a few days later. The 33-year-old Portuguese midfielder, who heroically recovered from a third knee injury of his career, was a crowd favourite, but the club didn't offer him a new contract and his No. 10 shirt was given to Giuliano, the talented Brazilian who impressed in his first season under Lucescu.

Incredibly, Giuliano too was gone just two months later, sold to Fenerbahce alongside Portuguese defender Neto. The No. 10 was then given to £12 million star Emiliano Rigoni, the fifth Argentinian recruit of the summer after Leandro Paredes, acquired from Roma for €23m, young striker Sebastian Driussi from River Plate for €15m, Lyon's Emanuel Mammana for €16m and defensive midfielder Matias Kranevitter from Atletico Madrid for €8m.

Paredes, who started the season in a very impressive fashion, jokingly nicknamed his new club "Zenit Junuors" but initially it was two Russian players who Mancini worked wonders with.

Aleksandr Kokorin, the problematic striker who had been written off by many as lazy and unprofessional, suddenly found some motivation and scored six goals in his first seven games. And Daler Kuzyaev, the anonymous midfielder whose arrival from Grozny went almost unnoticed, netted his first career goal on his debut and formed a good understanding with Paredes.

While Zenit didn't play especially well apart from the second half of the 5-1 thrashing of Spartak, they took 27 points from the first 11 matches, conceding just three goals, and opened a healthy gap at the top. Anything other than an easy march to the title looked unthinkable at that stage.

Then, in the beginning of October, disaster struck. Konstantin Sarsania, the sporting director responsible for assembling the squad, died unexpectedly at the age of 49 and Zenit lost their way.

Sarsania was highly influential at the club. During his first spell as sporting director, he helped the president Sergey Fursenko and Dutch coach Dick Advocaat to build the team that won an historic first title in 2007 and the UEFA Cup in 2008. He then pursued a rather low-profile coaching career, but kept close ties with the club and when Fursenko returned in May 2017, the president's most important condition was to get Sarsania back at Zenit.

"Sarsania's biggest talent was to find a way to everyone's heart," Ivan Zhidkov, editor-in-chief at St Petersburg newspaper Sport Den Za Dnem, told ESPN FC. "Mancini was initially a bit suspicious towards him, but quickly understood his worth. The sporting director was the main link between the president and the coach, and between the coach and the Russian players. He was Fursenko's right hand man. Without him, nothing worked anymore."

Zenit St Petersburg fans watched their team crumble after Sarsania's unexpected death. Alexander Demianchuk\TASS via Getty Images

It started with their first defeat of the season, at home to the modest Arsenal Tula, and continued with the 3-0 debacle against the resurgent Lokomotiv Moscow. Suddenly the team fell apart: Kokorin stopped scoring, Paredes' form was unrecognisable, Kuzyaev was played out of position and rumours of dressing room unrest appeared in the media.

One of the major conflicts was reportedly between Mancini and two leading Russian players, Artyom Dzyuba and Oleg Shatov, who complained they were being underused. Both were eventually loaned out in the winter break -- to Arsenal Tula and Krasnodar respectively -- but took their revenge by scoring against Zenit to deny them points in a 3-3 draw and 2-1 defeat.

Mammana then tore knee ligaments in March and Kokorin soon suffered the same fate. Dzyuba was replaced by the technically limited Anton Zabolotny, who was signed from tiny Tosno and didn't find the net even once. Mancini's side failed to score in 11 out of 29 league fixtures, including eight 0-0 draws to date.

Unable to find an answer, Mancini failed to impose any style on his team, but instead criticised players and management during his news conferences.

"Only Kokorin is able to score. I asked to buy other strikers, but that didn't happen," he said in March, hardly improving team morale. When asked by journalists about his so-called "whining," the Italian replied: "I am not whining. You are whining that I am whining."

Knocked out of the Europa League by RB Leipzig, the coach lost control and since Sarsania passed away the club have won just five out of 17 league matches. Their points total will be the lowest since 2008.

"With Sarsania, Zenit would definitely have fought for the title until the end," Zhidkov added. "Mancini wasn't loyal to Fursenko after the sporting director died, and his mind was mostly bothered with the Italy national team vacancy that opened in November."

Now the Gazprom giants will have to play in Europa League for the third season running, and yet another revolution is surely coming in the summer. Finding the right coach appears to be the first problem, but replacing Sarsania could be even harder.