Tottenham Hotspur have not signed a player since bringing in Lucas Moura from PSG in January 2018.
However, Spurs are expected to do business in the transfer market this summer. They are expected to sign a right-back following disappointing campaigns from their current players in this position - Kieran Trippier and Serge Aurier.
Here are five things you need to know about the talented Japanese international.
He Featured at the 2018 World Cup
Sakai was part of the Japan side that reached round of 16 at the 2018 World Cup in Russia, appearing in all four of their games.
Japan almost caused a monumental upset in their round of 16 clash with Belgium, going 2-0 up with 52 minutes on the clock.
Unfortunately for Sakai and Japan they could not hold on, with Belgium coming back to win 3-2, scoring the winner deep into injury time.
He's an Olympian
Sakai is one of the few players that is still plying his trade to have featured in both a World Cup and in the Olympic Games.
He was part of the Japan side that reached the semi-finals of the men's football tournament at the 2012 Summer Olympics in London.
The 29-year-old featured in four games as Japan finished in fourth place overall, missing out on a medal after losing the bronze to South Korea.
He Can Play Anywhere in Defence
On paper, the signing of 29-year-old Sakai might seem a little strange for Tottenham fans, considering manager Mauricio Pochettino has shown a preference for bringing in younger players.
However, Sakai's versatility may be one of the key factors in Spurs' interest. He is capable of playing anywhere across the back line, featuring at left-back and at centre-back for his clubs and his country throughout his career.
He Has the Attributes to Thrive at Spurs
Pochettino has won many admirers with his attractive brand of football at Tottenham, turning Spurs into a team that consistently finishes in the top four of the Premier League and also guiding them to the Champions League final this season.
The Argentine has deployed a high-pressing, high energy game at Tottenham and Sakai has the attributes to thrive at the north London side.
Sakai is technically sound, physically strong and has excellent stamina. The latter can be shown through the number of games he has played in recent campaigns - he has featured in 121 games in all competitions for Marseille across the last three seasons.
He Is a Published Author
While many footballers have written autobiographies, not many have penned books about sports psychology.
Sakai has done exactly that, in 2016 he published his first book, "Resetting Power 'Nature and the Mind Becomes Stronger' 46 Concept".
If Sakai could showcase these analytical traits on the pitch, Spurs are sure to benefit greatly.