Dele Alli apologised to team-mates and Gent midfielder Brecht Dejaegere for his reckless tackle as 10-man Tottenham crashed out of the Europa League.
Spurs needed to win by two after Gent's 1-0 victory in Belgium last week but Alli's 39th-minute lunge on Dejaegere, and subsequent sending off, made the task all the more difficult at Wembley.
Christian Eriksen's opener and an own-goal from Harry Kane meant the score was 1-1 when Alli was given his marching orders by referee Manuel De Sousa.
Victor Wanyama's superb second-half strike gave Tottenham hope but Jeremy Perbet's late goal on the break sealed Gent a 2-2 draw and 3-2 win on aggregate.