Pep Guardiola faces a testing week that could prove crucial in arresting Manchester City’s slump and reviving the defence of their Premier League title.

City end 2018 with a testing visit to Southampton before opening 2019 with leaders Liverpool coming to the Etihad, a game in which defeat for City could leave them 10 or more points off first place.

Such an outcome could prompt Guardiola to have a change of heart and invest in new blood in the January transfer window to try and revive their title challenge.

City’s sudden collapse, with three defeats in their last four Premier League games, has been blamed on the absence of injured holding midfielder Fernandinho and the lack of a suitable replacement.

The continued injury problems of French left-back Benjamin Mendy, and the recent loss of form of right-back Kyle Walker, have also presented Guardiola with a problem in the positions that are so key to his swashbuckling style of play.

Mendy’s replacement Fabian Delph has turned in some sub-par displays and was sent off in City’s most recent loss, at Leicester, earning him a three-match suspension.

All of which begs the question as to whether the self-styled world’s wealthiest club will invest heavily in the transfer window.

The Champions League, not won by Guardiola since Barcelona triumphed in 2011, remains a burning priority for the manager and the club’s Abu Dhabi owners, even though publicly they claim the Premier League title is their major target.

Guardiola has always insisted he will do no business in this window, waiting until the summer to strengthen a squad that, until the current run, looked deep enough to cope with any number of injuries or loss of form.

“When we created the squad at the beginning of the season, it was not to go to the January window except if we have problems,” said Guardiola last month.

“But I have a deep squad and a lot of players cannot play when I trust them a lot. They believe I don’t like them but that is not true.”

– ‘Dramatic loss of form’ –

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Now, City appear to have those “problems” to which Guardiola referred and there is a distinct possibility that City will move to stem the current “crisis” by signing either midfield cover or a new left-back in the coming month.

The former, certainly, is a major issue and one Guardiola tried to address in the summer with interest in Fred and, in particular, Jorginho before the duo chose to join Manchester United and Chelsea, respectively.

Tanguy Ndombele, the Lyon midfielder who impressed in his two meetings with City in the Champions League group stage this season, claimed this month Guardiola had tried to sign him in the summer.

The fact that UEFA have abolished the cup-tied rule for this season’s competitions also means Ndombele could play for City in the knock-out stages of the Champions League.

With a summer move for the player looking inevitable, there is the distinct possibility the English club could try to move the transfer forward by six months.

Full-back remains a more complicated issue and, having spent over million (USD 159 million) in little over a week in the summer of 2017 in signing Mendy, Walker and Brazilian Danilo, it is an area that should not need strengthening.

For this week, Guardiola has to come up with a solution at left-back.

Converted midfielder Oleksandr Zinchenko is a possible replacement for the suspended Delph but the Ukrainian is another player to be suffering a dramatic loss of form at present.

Brazilian Danilo, very much a back-up last season, can play either full-back position if Guardiola is not tempted to recall Walker following a couple of torrid recent outings.