In the 2018–19 season, Dier scored his first goal of the season, which is his first in 18 months, in the 1–0 win against Cardiff City, helping Tottenham to their joint best start of a season in the Premier League after eight games. He underwent surgery mid-December 2018 due to appendicitis, and returned to the team on 20 January 2019, coming on as a substitute in the game against Fulham. However, he continued to suffer the after-effects of the appendicitis operation, repeatedly falling ill and missing games. On 1 June, in Tottenham's first appearance in the Champions League final, Dier replaced the injured Moussa Sissoko for the final 16 minutes of a 2–0 loss to Liverpool in Madrid.