The video, obtained by DailyMail shows the Cleveland Cavaliers player getting cosy with a brunette woman.
The publication claims the pictures and video of Thompson appearing to kiss a mystery brunette in a New York City club occurred on Saturday, April 7.
Khloe and Tristan confirmed in September that they were expecting their first child.
'My greatest dream realized!' the Keeping Up With The Kardashians star said at the time. 'Tristan, thank you for loving me the way you do! Thank you for treating me like a Queen. Thank you for making me feel beautiful at all stages! Tristan, most of all, Thank you for making me a MOMMY!!!! You have made this experience even more magical than I could have envisioned! I will never forget how wonderful you’ve been to me during this time. Thank you for making me so happy my love!'
Neither Khloe or Tristan have responded to the shocking video.