Antonio Conte's squad took to the field at the Seoul World Cup Stadium for training on Monday with most of their internationals in tow, including Sweden's Kulusevski.
Players were subjected to a particularly taxing session in sweltering temperatures, and those in attendance in the stands witnesses members of Conte's squad suffering during a gruelling fitness exercise.
Crowd favourite Son Heung-min collapsed while Harry Kane was pictured vomiting after the squad completed approximately 40 lengths of the pitch after a two-hour session.
However, Kulusevski was seen speaking to Tottenham medical staff before leaving the pitch earlier in the session, and The Telegraph claims that the attacker pulled up with a calf injury.
The severity of the 22-year-old's issue is unclear at this point, but he has emerged as a doubt for Tottenham's opening game of pre-season with the K-League XI on Wednesday afternoon.
Kulusevski made an immediate impression at Tottenham after arriving on loan from Juventus in January, recording five goals and eight assists in 18 Premier League appearances.
The Sweden international is still only on loan at the club from Juventus, but he is expected to make his move to the club permanent at the end of next season.
In spite of Conte's brutal practice session, Tottenham appeared to finish the session otherwise unscathed and boasting a strong squad for their first pre-season contest.
New signings Richarlison, Yves Bissouma, Ivan Perisic and Fraser Forster have all made the journey, but Clement Lenglet's documentation was not sorted in time for the Barcelona loanee to travel.
Joe Rodon has also not made the journey to South Korea due to illness, but the Welshman is being strongly linked with a move away from the club in the current window.
The quartet of Harry Winks, Giovani Lo Celso, Sergio Reguilon and Tanguy Ndombele have also been left at home as the quartet aim to secure their own summer transfers elsewhere.
Following their clash with the K-League XI, Tottenham will also battle Sevilla in the Coupang Play Series on Saturday at the Suwon World Cup Stadium.
Conte's side will then travel to Glasgow to face Rangers before rounding off their pre-season against Roma in Israel in the I-Tech Cup, which will see the Lilywhites reunite with former manager Jose Mourinho.