While Francesco Calzona made an immediate impact by helping his new side hold Barcelona in the Champions League, Ranieri's men are mired inside the relegation zone after five games without a win.
Match preview
Swiftly replacing the sacked Walter Mazzarri, just two days before Napoli's last-16 tie in the Champions League, Slovakia manager Francesco Calzona stepped into the Stadio Maradona dugout on a short-term deal, and the ailing Azzurri responded with a fightback to avoid first-leg defeat.
Following previous spells in Naples as assistant manager and coach, Calzona's debut in the top job saw Victor Osimhen produce a crucial equaliser on his return to club duty, following an extended stay with Africa Cup of Nations finalists Nigeria.
The Italian champions are therefore level with their Spanish counterparts ahead of next month's return leg in Barcelona, so attention can now switch to reviving their dire domestic situation.
In real danger of missing out on European qualification, Mazzarri's final game in charge proved to be last Saturday's 1-1 home draw with Genoa, when only a late leveller from Cyril Ngonge snatched the point that kept the Scudetto holders ninth in the table.
That was only Napoli's third goal in five matches, so Osimhen's return has been warmly welcomed by a restless fanbase, who have seen their side accrue 29 points fewer than after 25 league games last season: no reigning champions have ever posted such a negative difference at this stage of a title defence.
Highlighting their attacking woes without Osimhen, and with last year's Serie A MVP Khvicha Kvaratskhelia still failing to produce his best, the Azzurri have not scored for five away fixtures ahead of their trip to Sardinia. At least a fine recent record in Cagliari can offer some solace to Calzona: Napoli have won six of their last seven away games against Sunday's hosts, averaging almost three goals per game.
Indeed, Cagliari have won just one of their last 25 top-flight matches against Napoli, losing no fewer than 17 and scoring at a measly rate of only a goal every other game.
The Rossoblu's veteran coach Claudio Ranieri now reconvenes with one of many former clubs, seeking points to help his side stay afloat in Serie A following promotion through the playoffs.
A streak of four straight losses - to Frosinone, Torino, Roma and Lazio - left Cagliari languishing in the bottom three ahead of last week's clash with draw specialists Udinese, but Napoli loanee Gianluca Gaetano found the net in a 1-1 result that at least ended their run of defeats.
Upcoming fixtures against relegation rivals Empoli and Salernitana could prove pivotal in deciding the Isolani's destiny, but first they must tackle a team that, for all their faults, still possess plenty of firepower and may be rejuvenated under new management.
After previously putting together a superb sequence of four wins and two draws at home, Cagliari have since lost their last two fixtures on Sardinian soil, and the odds will be against them suffering an unwanted hat-trick in that regard.
Cagliari Serie A form:
W
L
L
L
L
D
Napoli Serie A form:
L
W
D
W
L
D
Napoli form (all competitions):
L
D
W
L
D
D
Team News
After Walter Mazzarri tinkered with a three-man defence several times towards the end of his doomed second spell as Napoli coach, Francesco Calzona reverted to the Campanian club's familiar 4-3-3 formation in midweek, with main marksman Victor Osimhen as its spearhead.
Set for his first Serie A start in several weeks, Osimhen has found the net in all four previous encounters with Cagliari, against whom he scored his last league goal in mid-December.
Cyril Ngonge missed Wednesday's game due to a muscle strain suffered in training and remains a major doubt, while captain Giovanni Di Lorenzo is sidelined by suspension; however, Piotr Zielinski - who was omitted from the UEFA squad list after failing to sign a new deal in Naples - could come back into contention.
Meanwhile, the visitors will be without injured quartet Eldor Shomurodov, Marco Mancosu, Pantelis Chatzidiakos and Gaetano Oristanio this weekend.
Claudio Ranieri frequently rotates his resources up front, but Napoli-owned Gianluca Gaetano is sure to play a part: since making his debut earlier this month, he has scored two goals in three appearances, in addition to creating more chances (five) and completing more dribbles (five) than any other Cagliari player.
Cagliari possible starting lineup:
Scuffet; Zappa, Mina, Dossena, Augello; Nandez, Makoumbou, Jankto, Luvumbo; Gaetano; Lapadula
Napoli possible starting lineup:
Meret; Mazzocchi, Rrahmani, Jesus, Rui; Anguissa, Lobotka, Traore; Politano, Osimhen, Kvaratskhelia