Spanish giants Barca have won back-to-back matches since losing to Chelsea in their opening summer outing, while Napoli have won three of their five friendlies so far.
Napoli's Serie A campaign does not begin until August 24 with a trip to Fiorentina, but they are already at an advanced staged in their pre-season preparations.
Unbeaten in four games, three of those ending in victory, Napoli will be looking to claim a big scalp Stateside as they take on Spanish giants Barcelona in back-to-back matches.
Ancelotti only has these two matches left before the Serie A opener with Fiorentina in just under three weeks' time, and games do not come tougher than this.
Following the arrival of Konstantinos Manolas in the heart of defence and Eljif Elmas in midfield, combined with the stability of keeping Ancelotti in place, Napoli will be hoping to build on last term's second-placed finish in Serie A.
A victory over Barca on Thursday would be a good way to lay down a marker for the season ahead.
Form in pre-season: LWDWW
Barcelona's results have got gradually better during pre-season, most recently beating Arsenal 2-1 at Camp Nou on Sunday to retain the Joan Gamper trophy.
Pierre-Emerick Aubameyang gave Arsenal a first-half lead in Catalonia, but a disastrous own goal from Ainsley Maitland-Niles and a late Luis Suarez strike gave Barca their second win on the bounce, following the 2-0 victory against Vissel Kobe in Japan.
Those wins came on the back of a 2-1 loss to Chelsea in their opening pre-season outing, though the Blues were at a more advanced stage in their summer programme at that point.
Messi did not make it off the bench against Arsenal and he will have to wait a little while longer for his first appearance of pre-season as he has not travelled to the United States with the rest of the squad, which includes a few academy players.
An injury sustained in training means that the Argentina international, who was in Copa America action as late as July 6, will not have played a single minute of club action before the La Liga opener against Athletic Bilbao in two weeks' time.
Others have been given a chance to impress in Messi's absence, though, and the performance from summer signing Frenkie de Jong on his full debut against Arsenal is a major positive, even if he suggested after the match that he was unhappy with his display.
De Jong will be hoping to get another couple of starts under his belt this week, while Antoine Griezmann is another in need of more minutes before the real business gets up and running.
With those two newbies to factor in, Valverde will use these back-to-back matches against Napoli - in Florida and Michigan - to settle on his preferred XI for the start of the new campaign.
Form in pre-season: LLWW
Messi's absence is a major blow for Valverde, who would have targeted these games against Napoli as an opportunity to use him alongside Griezmann and Suarez.
Getting Griezmann and De Jong integrated into the starting lineup will be next on Valverde's list of priorities, with both players in line to retain their places on Thursday.
As for Napoli, Piotr Zielinski pulled out of the last friendly with illness and it remains to be seen whether he will be fit enough to play a part in Florida.
Star defender Kalidou Koulibaly, who now looks set to stay in Naples for another year, is back in contention after his extended break on the back of Senegal's Africa Cup of Nations campaign.
Ancelotti made six changes at half time against Marseille, including the introduction of Younes and Giovanni Di Lorenzo, but with time ticking down to the start of the new season he may field something close to his strongest possible XI from the off.
Napoli possible starting lineup:
Meret; Di Lorenzo, Manolas, Maksimovic, Rui; Callejon, Ruiz, Verdi, Younes; Insigne, Milik
Barcelona possible starting lineup:
Ter Stegen; Semedo, Pique, Umtiti, Alba; Rakitic, De Jong, Puig; Dembele, Suarez, Griezmann
Head To Head
Napoli and Barcelona have avoided each other in European competition, but they have met a couple of times in friendlies over the past eight years.
The Italian side won 1-0 when the sides faced off in August 2014 through a Blerim Dzemaili goal 10 minutes from time.
That was revenge of sorts for the 5-0 thrashing Barca inflicted on them in their only other encounter three years prior - Cesc Fabregas scoring his first goal for the La Liga club that day.
We say: Napoli 1-1 Barcelona
Both sides head into this match on the back of successive wins but Napoli look to be at a more advanced stage in their preparations for the new campaign, even if their first competitive match is a week after Barcelona's.
The absence of Messi is also a big positive for Ancelotti's men, but it will still be a big ask to overcome Barca in the first of these two Stateside friendlies.
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