Claudio Ranieri’s greeting for Kasper Schmeichel on Thursday was also the most tender of fitness tests. Until then the goalkeeper had offered the manager only his left hand since fracturing his right one in the Champions League draw at FC Copenhagen on 2 November but now Ranieri decided it was time to step up the comeback. “I said: ‘Give me the right’ and I shook it – but gently,” said Ranieri.

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Schmeichel survived. Now Ranieri is taking encouragement from the belief that his first-choice goalkeeper, who is still training separately from his team-mates, could be back in action before Christmas. But there is no definite return date. “It depends on him and the surgeon,” said Ranieri. So Ron-Robert Zieler will remain in goal for another few weeks at least. And the German has been jittery since standing in for Schmeichel – one reason why the champions have slipped into such a Premier League rut that Ranieri bills Saturday’s duel with Sunderland as a relegation battle.

Zieler was one of six signings Leicester made in the summer as they spent over £60m in an effort to defend their title and make waves on their Champions League debut. Only one, the Algerian striker Islam Slimani, can be classed as a success and even he has not been a perfect fit.

Nampalys Mendy, prised from Nice as the intended solution to one of football’s toughest brain-teasers – how do you replace N’Golo Kanté? – has only just returned to full training after injuring his ankle in the defeat at Hull City on the opening day of the season. Ranieri is considering taking him to Sunderland as a substitute. The Nigeria winger Ahmed Musa has performed only fitfully. The defender Luis Hernández has not made a league appearance since the 3-0 walloping at Chelsea in mid-October. And Bartosz Kapustka, the 19-year-old Polish midfielder, has not played at all, with Ranieri saying he is not yet robust enough for the Premier League.

The Italian defends this recruitment and explained that some players need a while to adapt to the Premier League, citing the example of Riyad Mahrez, who was gradually integrated into English football after arriving from Le Havre in 2014. “If he needed six or seven months, imagine [how it is] for the others,” said Ranieri. Which is fair enough. The problem is that the performances of Leicester’s established players this season suggest the club needed summer reinforcements who were ready for immediate deployment in the Premier League. Especially as the most promising youngsters already at the club have not yet been able to contribute as much as hoped. The 19-year-old full-back Ben Chilwell suffered an ankle injury from which he has only just recovered, while Ranieri has deemed another youngster, the winger Demarai Gray, to be ready for no more than one league start so far this season despite some impressive appearances from the bench.

Ranieri said after the match at Watford three weeks ago – their fifth defeat from six Premier League away matches – that he would give more serious thought than ever to revamping his starting line-up. But he made only one alteration for the next league match, Saturday’s home draw with Middlesbrough, and that was enforced by the suspension of Danny Drinkwater. The manager does seem unconvinced about his squad’s depth – players cannot return from injury soon enough.

Jamie Vardy is not scoring, partially because Leicester are not creating many chances for him. Mahrez has completed only two passes to the England international in the last eight league matches combined, an extraordinary statistic given how thrillingly they colluded last season. Ranieri admits his team are not clicking but is reassured, at least, that this is not due to a drop in motivation. “If we compare with last season, we are missing everything,” he concedes. “But the spirit is the same.”

Facebook Twitter Pinterest Ron-Robert Zieler has been a jittery presence in the Leicester goal in the absence of first-choice Kasper Schmeichel. Photograph: Plumb Images/Leicester City FC via Getty Images

The loss of Schmeichel has been a particular blow because, until his injury, he was the only Leicester player whose performances this season had reached the same level as last. Not only was he still making terrific saves; he was distributing the ball as well as ever and reassuring his defenders while There has been little sign of Zieler seems to have compounded the uncertainty of defenders already adapting their approach to take account of referees’ new vigilance for grappling in the box.

So far Ranieri’s attempts to make his side more solid have included only one quickly aborted change of formation. A switch to a back three – a pattern that succeeded for Nigel Pearson during Leicester’s late surge clear of relegation trouble in the 2014-15 season – was abandoned early in the game against Copenhagen because the team seemed to be destabilised even more by it. Hernández, drafted back into the starting lineup, looked particularly lost.

Ranieri hinted on Thursday that improved defensive options may be on his January shopping list. The forthcoming transfer window will be the first since the appointment of the former Liverpool scout Eduardo Macia as head of recruitment in place of Steve Walsh, who was lured to Everton.

Leicester need at least some of next month’s signings to pay off faster than their summer ones. It would be a boon if Wilfred Ndidi turned out to be a ready-made replacement for Kanté. But the Genk midfielder is only 19. Still, Leicester are close to agreeing a transfer of around £15m for him and will be thankful Nigeria have not qualified for next month’s Africa Cup of Nations. But Leicester look set to be affected by that tournament more severely than any other Premier League club as they are likely to lose Ghana’s Daniel Amartey as well as Algeria’s Mahrez and Slimani.