On 13 September 2020, Lee became the youngest player, aged 19 years and 207 days, to assist two goals in a La Liga match in the 21st century, in a 4–2 win over Levante, breaking the previous record of Juan Mata in 2008, aged 20 years and 150 days. Despite rejecting several renewal offers from the club throughout the year, he featured regularly under Javi Gracia as the "Che" ended the campaign on a mid-table position.