The Algeria striker tried to force a move after the World Cup but the Portuguese club refused to cave in and he will offer a potent threat alongside Nani in Tuesday’s Champions League match

Over at Sporting Lisbon the scenario felt depressingly familiar. Last season had yielded a fine second-place finish behind Benfica and qualification for the Champions League, only to give way to another unsettling summer as players were cherry-picked by richer rivals or threatened to be prised away.

Eric Dier left for Tottenham Hotspur, William Carvalho drew plenty of admiring glances, while Marcos Rojo agitated more shamelessly for a move to Manchester United. The Argentinian’s stance infuriated the club’s president, Bruno de Carvalho, yet where the defender was permitted to leave, another player was denied his departure. That dissident, reintegrated after all the discord and revived back in the side, is now intent on wounding Chelsea.

There was a time this summer when Islam Slimani must have felt untouchable. A key member of Vahid Halilhodzic’s Algeria squad at the summer’s World Cup, he had scored goals against South Korea and Russia in the group to thrust his country into the knockout phase for the first time in their history. In the last 16 he had a header disallowed against Germany, and later forced Manuel Neuer into a fine save, as the Desert Foxes took the eventual world champions into extra time before succumbing with heads held high. They returned home as heroes with reputations enhanced. The 26-year-old with 12 goals from 24 caps, in particular, had alerted scouts around the globe as to his qualities.

Slimani is the kind of athletic, workaholic forward around whom a team’s style and strategy can be built. At 6ft 2in he is strong in the air, as Russia and numerous opponents in the Primeira Liga have discovered, and boasts deceptive pace.

The Portuguese coach and manager of Ethiopia, Mariano Barreto, had pressed the striker’s credentials to Sporting a year ago when he was still a relative unknown at Chabab Riadhi de Bélouizdad in Algiers. “Slimani is a mixture of Mário Jardel and [the prolific former Sporting forward] Liédson: a very fine header of the ball, quick and with a powerful shot from a short back-lift,” he said. “He may not be as deadly a finisher as Jardel but there’s more aggression to his game and he works so hard for his team. He keeps going, harassing defenders. He was a revelation last season, and confirmed his ability at the World Cup.”

Leicester City and West Ham emerged as contenders to lure the forward to the Premier League. Schalke, Champions League rivals in Sporting’s group, considered him a tempting recruit, while Halilhodzic sought to be reunited with the striker at his new club, Trabzonspor, having departed his position with Algeria much to the disappointment of the national federation.

Slimani watched the interest roll in, the offers on the table tantalising for a player earning a basic £4,000-a-week. At the very least he expected a hefty pay rise to reflect his new standing within the game. With suitors queuing up from the Premier League to the Bundesliga for a player who had started 26 league games for Sporting last season, scoring eight goals, life at the Estádio José Alvalade suddenly felt rather unfulfilling.

Yet De Carvalho had other ideas. The cases of Rojo and Slimani became Sporting’s cause célèbre of the summer, the hierarchy outraged at perceived “breaches of contractual duties” given their clear desire to leave. The players were under contract until 2017 and the club had no intention of being bullied into sales by agents, third-party ownership funds and rival clubs alike. Or by the players themselves.

The president’s reaction to what amounted to transfer requests from his left-back and centre-forward was to banish each to the fringes. “They are, for now, training away from the first-team and won’t be training with the B, C or D teams either,” he had said only four days before the start of the domestic season. “Both players made decisions that led to them being the subject of strong disciplinary measures. We won’t tolerate blackmail or pressure from outside, and we certainly won’t give in to agents and funds.”

De Carvalho, a lifelong supporter who was elected Sporting president in March 2013, has become a crusader against investor funds who have bought into the economic rights of footballers, arguing they are a “monster” and a “menace” and undermine football’s integrity. Much of his fury was directed at Doyen Sports, the offshore fund which claimed it was entitled to 75% of the £16m that took Rojo to Old Trafford.

Slimani’s case was more conventional, a player late to life in one of Europe’s main leagues and whose head had been turned. Sporting made it known they would hold interested parties to the £24m buy-out clause in his contract. None of the offers on the table came close.

As an attempt to placate a disaffected yet important player, Sporting offered improved terms upping his salary to nearer £7,000-a-week. Yet, for a while, Slimani held firm and endured life as an outcast. Barreto spoke with the player and suggested he was “sad and hurt” at finding himself ostracised. The forward perceived his punishment to be unfair, his claim for better recognition in his contract justified. “I don’t think he realised what would happen,” said the Ethiopia coach. “Sporting needed Slimani, and the player did not understand he needed them too. He was clearly ill-advised.”

Perhaps the forward had naively assumed the club would merely cave in. After all, he had first-hand experience of getting his own way. Look back in his career and the striker, having initially made his mark with the amateur club Jeunesse Sportive Madinet de Chéraga in the Algerian third division, had been brought to Algiers for £8,000 by Bélouizdad, the six-times national champions. There were four seasons spent at Stade du 20 Août 1955, his progress steady with 43 goals in 122 games before, in the summer of 2013, the man nicknamed “Super Slim” determined the time was right for a move.

Nantes had offered him the chance of a fresh start in France and, with Bélouizdad reluctant to entertain his departure for the fee on offer given he had 12 months to run on his contract, Slimani took the club to court claiming a pledge to provide him with an apartment had not been honoured. The Algerian football federation ruled in his favour and, much to Bélouizdad’s frustration, he was permitted to leave on a free transfer. The twist was, unbeknown to Nantes, Sporting had stepped in once it was clear there would be no transfer fee with their contract offer trumping that of the French club. Waldemar Kita, the Nantes president, described Slimani’s attitude as “scandalous” when he was unveiled in Lisbon.

Player power had prevailed then. The Algerian hoped it would again a year later. Yet all it took this time round was 12 days of a hard-line approach, with the threat of life out of the limelight after all that success in the summer, for the striker to reconsider. On 23 August the club announced he had issued an apology, acknowledging he had “not acted in a correct and professional manner” but was now “showing remorse for his behaviour”.

The statement, hammering home the point, was “a formalised recognition of his guilt” with the player reinstated “without prejudice” into the senior set-up. His first game back was at Benfica eight days later as Europe counted down the hours to the transfer deadline. He equalised 19 minutes into the derby, tapping in after Nani had panicked the home goalkeeper, Artur, into a horrible error at a clearance. The badge kissing in front of the away contingent was predictable.

Behind the scenes, the truce appears to have been brokered with compromise on both sides. Slimani has his slightly improved contract and, more significantly, a verbal agreement he will be allowed to leave at the end of the season if an acceptable bid – not necessarily matching his release clause – is lodged.

Sporting have their most imposing forward content and restored to operate in tandem with Nani. For now the striker is the first player developed by an Algerian club to compete in the Champions League since Auxerre’s Abdelhafid Tasfaout in 1996-97. He is eager now to leave his mark on this competition. Chelsea should beware.