Leeds have opened formal talks with the French club over a deal for the 25-year-old, though the fee being demanded remains a sticking point in negotiations. Everton have also been credited with an interest in the player, along with Nottingham Forest, Tottenham and Aston Villa, who tracked his progress even before his move to Ligue 1 last year.
Lyon signed Sulc from Viktoria Plzen last summer for around £6.5m, and he went on to enjoy an outstanding debut campaign in France, scoring 15 goals and providing 10 assists in 42 appearances across all competitions. Those performances have made him one of head coach Paulo Fonseca's most important players and triggered widespread interest from clubs across Europe.
Sulc was part of the Czech Republic's squad at this summer's World Cup in the United States, having established himself as a regular for his country. He is under contract at Lyon until 2029, giving the French club a strong negotiating position, though their well-documented financial difficulties mean a sale this summer cannot be ruled out if the right offer arrives.
Lyon are reluctant to lose a player they view as central to their plans, with the club preparing for a Champions League third qualifying round tie in early August. Any suitor will therefore have to match, or come close to, Lyon's valuation if they are to prise Sulc away from the Groupama Stadium before the transfer window closes.
Leeds United had already been keeping tabs on Sulc before this summer, having shown initial interest last year prior to his move from the Czech top flight. Daniel Farke's side have been busy in the transfer market so far this window, bringing in Harry Wilson on a free transfer from Fulham and defender Tarik Muharemovic from Sassuolo, and appear determined not to let the valuation gap derail their pursuit.
Sulc, capable of playing across the front line as well as centrally, has 18 caps for the Czech Republic. His versatility and eye for goal have made him a target well beyond Leeds, with Crystal Palace also credited with interest.