Carlos Alcaraz will start his US Open title defence against Russia's Roman Safiullin in the first serious examination of his fitness following a long-term wrist injury.
Second seed Alcaraz, who won the men's title in New York last year, has not played a competitive singles match for more than four months because of inflammation in his playing right wrist.
Despite his lack of action, the 23-year-old Spaniard is still considered by many as the favourite to triumph again - particularly because his great rival Jannik Sinner is not playing due to a knee injury.
The pair may have been a cut above the rest of the tour for the past two seasons, but Alcaraz coming back from a prolonged absence with such a delicate injury and beating the rest of the field - even though he is a generational talent - would be remarkable.
The seven-time major champion missed this season's French Open and Wimbledon as a result of the injury, which did not require surgery, before making his return to court in the US Open mixed doubles alongside Serena Williams earlier this week.
Wearing a long compression sleeve on his right arm, Alcaraz did not look totally convincing in the exhibition-like event. Understandably, he appeared to be holding back on his serve and return as he eased himself back into matchplay.
There is no doubt that a Grand Slam singles bout played over five sets will be another step up physically. Safiullin, with a hefty serve and attacking groundstrokes, is not an ideal opponent to start against.
The 29-year-old Russian, who reached the Wimbledon fourth round last month before falling to Novak Djokovic, is likely to take time away from Alcaraz, test the Spaniard's durability at the baseline and generally make him feel uncomfortable.
Predicting how Slam draws will pan out is always a fool's errand, but if Alcaraz does get past Safiullin and goes as far as the fourth round, there are more potential opponents who appear daunting given the length of his absence.
If you analyse Alcaraz's projected draw by the seedings, he could face rock solid American Tommy Paul or unpredictable Kazak Alexander Bublik in the last 16.
Athletic Frenchman Arthur Fils and huge-serving Ben Shelton are potential quarter-final opponents. Djokovic could lie in wait in the semi-finals.
Nobody outside of Alcaraz and his core team knows how his wrist is likely to stand up to the rigours of playing five-set matches in the heat of a Grand Slam tournament.
A challenging start at Flushing Meadows and a potentially intimidating second week will tell us.