Andrea Pirlo's Juventus face a key test of their ambitions to clinch a 10th consecutive Serie A title in a packed January of football in Italy after a stuttering start which has left the holders sixth in the league.
Serie A returns this weekend after the mini-break of the Christmas period with a tight January schedule.
Juventus host Udinese on Sunday before taking on three of the top four this month, with six Serie A fixtures in addition to Italian Cup and SuperCup commitments.
The two Milan clubs -- the only teams apart from Juventus to have won the league in the past two decades -- are on top as they look to bring the title back to Lombardy.
AC Milan are flying high one point ahead of Antonio Conte's Inter with Roma in third, six points off second place.
Juventus are sixth, 10 points adrift of top spot, but having played a game less.
After Udinese, Juventus visit AC Milan in the San Siro next Wednesday before hosting fourth-placed Sassuolo in Turin followed by a trip to play Inter.
Despite topping their Champions League group, Juventus have struggled for consistency on the domestic front, relying on Cristiano Ronaldo's goals.
The Portuguese striker has scored 12 of Juventus's 25 league goals this campaign.
In the league, they have six draws and six wins, falling to their first league defeat of the season 3-0 to Fiorentina at home before Christmas.
"Sometimes it happens we're not 100 percent. Now we have to start again with desire, thinking about the mistakes we made and carrying out our project," said Pirlo.
The former Italy and Juventus star can take heart from the fact that in the 2015-2016 season, they were 12th after ten matches, but powered back to win the title.
"It's premature to talk about the title," said Milan coach Stefano Pioli.
"Juventus remain favourites, a team that in the last nine years have won as many titles and have many champions.
"But there is also Inter, who came within one point of Juve last year and spent a lot of money in the transfer market. In addition, Inter have no European commitments."
Both Milan teams return against two promoted clubs.
AC Milan, without injured Zlatan Ibrahimovic for a seventh consecutive league game, look to continue their unbeaten run at midtable Benevento, as Inter Milan host struggling Crotone.
Behind the leaders, Roma host former coach Claudio Ranieri's Sampdoria, who are in 11th.
Fourth-placed Sassuolo travel to Atalanta, in seventh, for a clash between two attacking teams targeting European football.
Fifth-placed Napoli look to end their three-match winless run at Cagliari, but without injured forward Dries Mertens, defender Kalidou Koulibaly and striker Victor Osimhen, the Nigerian having tested positive for Covid-19, having been sidelined since November with a shoulder injury.
One to watch: Radja Nainggolan
Radja Nainggolan warned he wanted to have an impact on 15th-placed Cagliari after rejoining on a second loan from Inter Milan.
"I arrive in Cagliari with great desire, after three difficult months where I never saw the pitch," said the Belgian midfielder.
Nainggolan featured just four times in the league for Inter this campaign with less than an hour on the pitch in total.
The former Roma player has scored 13 goals for Cagliari, where he also played from 2010-2014, including six last season.
Cagliari are without a win in two months.
26 - Sassuolo's points after 14 games, a record for the club
12 - Cristiano Ronaldo leads the Serie A goal-scoring charts
7 - Inter Milan's winning streak
3 - Napoli's winless run
1 - Points between leaders Milan and Inter
Sunday (all times GMT)
Inter Milan v Crotone (1130), Atalanta v Sassuolo, Cagliari v Napoli, Fiorentina v Bologna, Genoa v Lazio, Parma v Torino, AS Roma v Sampdoria, Spezia v Hellas Verona (all 1400),Benevento v AC Milan (1700), Juventus v Udinese (1945).