Argentina vs. Saudi Arabia (Tuesday, 10.00am)
Concerns were immediately raised over the welfare of Messi when it was reported that the Paris Saint-Germain attacker was training individually on Saturday, but he is not reported to be suffering from any sort of injury and was back with the team the following day.
Lisandro Martinez and Exequiel Palacios were also restricted to indoor work a couple of days ago but should be fine for Tuesday, while Joaquin Correa has been forced to withdraw injured and has been replaced by Thiago Almada.
Assuming he is fit enough, Messi will expect to form an intimidating attacking trident with Lautaro Martinez and Angel Di Maria, while Cristian Romero and Nicolas Otamendi could line up at the back if Martinez is spared.
As for Saudi Arabia, five-cap midfielder Riyadh Sharahili has reportedly sustained a muscular problem which has thrown his World Cup hopes into doubt, while defender Hassan Tambakti is now back in full training after recovering from discomfort.
It would have been a surprise to see either man start against Argentina, though, and experienced attacker Fahad Al-Muwallad - who has 17 international goals to his name - was left out of the squad after failing a drugs test.
Star man Salem Al-Dawsari will expect to occupy the left flank for Saudi Arabia, as Saleh Al-Shehri - the joint top goalscorer in the third round of AFC qualifying with four strikes - starts on the opposite side.
> How Saudi Arabia could line up against Argentina
> How Argentina could line up against Saudi Arabia
> World Cup 2022: Argentina vs. Saudi Arabia head-to-head record
Denmark vs. Tunisia (Tuesday, 1.00pm)
Denmark finished with the joint-best defensive record in the World Cup qualifiers, where they conceded just three goals in 10 matches, and Hjulmand will hope for another defensive show of class from his side in Qatar.
That being said, we expect the 50-year-old to name a back four of Daniel Wass, Joachim Andersen, Barcelona man Andreas Christensen and full-back Joakim Maehle, shielding veteran Kasper Schmeichel in goal.
Manchester United summer signing Christian Eriksen, who is third in the nation's all-time appearance chart with 117 senior caps to his name, will be tasked with making things at the centre of the park, alongside Thomas Delaney and Tottenham man Pierre-Emile Hojbjerg.
Eriksen has racked up 39 goals for the Danes and should add extra threat in the attack, where Kasparov Dolberg, Mikkel Damsgaard and Andreas Skov Olsen, who has nine goals involvements in the Belgian top flight this season, will be pushing for starting roles.
Tunisia have named 26 players to represent the nation in Qatar, including Lorient defender Montassar Talbi, Youssef Msakni, who has 17 international goals, and Manchester United youngster Hannibal Mejbri.
However, the Carthage Eagles' squad is headlined by 31-year-old forward Wahbi Khazri, who is second in the nation's goalscoring chart with 24 goals in 72 appearances.
The Montpellier man will spearhead the attack on Tuesday alongside Msakni and 21-year-old Anis Ben Slimane, while we expect a back four of Mohamed Drager, Montassar Talbi, Dylan Bronn Ali Abdi, with Aymen Dahmen in goal.
> World Cup 2022: Denmark vs. Tunisia head-to-head record
Mexico vs. Poland (Tuesday, 4.00pm)
Star striker Raul Jimenez, who has scored 29 goals for Mexico, made his first appearance for almost three months when coming off the substitutes' bench at half-time of Mexico's 2-1 defeat to Sweden in a friendly on Wednesday.
The 31-year-old has not featured for Wolverhampton Wanderers since August due to an ongoing groin issue, which makes his place in the starting XI against Poland on Tuesday a serious doubt.
Henry Martin is ready and waiting to lead the line should Jimenez be deemed only fit enough for the bench, while Jesus Corona has been ruled out of the entire tournament due to an ankle injury.
Poland, meanwhile, have seen Bartlomiej Dragowski, Jacek Goralski and Adam Buksa withdraw from their squad due to injury.
Lewandowski was an unused substitute during his nation's 1-0 win against Chile in a friendly on Wednesday, with Michniewicz preferring to keep his talisman fresh for the tournament.
Aston Villa's Matty Cash, who only made his international debut a year ago after applying for a Polish passport through his mother's descent, should shake off a shoulder issue to be available for selection, but he faces plenty of competition at right wing-back.
> How Poland could line up against Mexico
> How Mexico could line up against Poland
France vs. Australia (Tuesday, 7.00pm)
Injury after injury after injury has been the theme for France even before the first ball has been kicked, with Saturday night's headlines being made after Karim Benzema was made to withdraw after picking up a thigh issue, having just returned to full training alongside Raphael Varane.
Deschamps will not name a replacement for Benzema, and he has also been forced to swap Presnel Kimpembe and Christopher Nkunku out for Axel Disasi and Randal Kolo Muani respectively.
Olivier Giroud, Antoine Griezmann, Kylian Mbappe and Ousmane Dembele are expected to form the attacking quartet in Benzema's absence, and with Varane possibly not being risked for the opening matchday, Ibrahima Konate and Dayot Upamecano could line up at the back.
Deschamps has affirmed that Varane is fit to start, though, while Eduardo Camavinga sat out training on Sunday with discomfort but should be fine for the opening day.
France are not the only ones to have been cursed on the injury front, as Hibernian striker Martin Boyle has been nursing a knee problem and has been forced to withdraw from the squad.
Marco Tilio has replaced the 29-year-old, and Arnold otherwise has all members of his squad fit and raring to go - Ajdin Hrustic has reportedly been working as normal recently following his own injury concern.
Stoke City defender Harry Souttar has affirmed that he is ready to feature on the opening matchday, despite a distinct lack of match practice since his ACL surgery, but Bailey Wright may be preferred from the off here as Souttar builds up his fitness.
> How Australia could line up against France
> How France could line up against Australia