Gustin told E! Online that the duo will have a confrontation in the upcoming Michael Jackson tribute.
"I'm a little bit of a bad boy and I inflict pain on somebody," he said.
"She comes to give me a piece of her mind. She comes to Dalton and [our performance of] 'Smooth Criminal' happens."
Gustin also revealed that he will be performing two Jackson tracks with The Warblers, including 'Bad', and joked that he understands why fans don't like his character.
"I know a lot people hate [him]," he joked. "I would too if I wasn't playing him, but I kind of do even though I am playing him!"
However, Gustin confessed that the role is "a lot of fun", adding that in a future episode he will "slushy two people".
Gustin, who may become a series regular on Glee's fourth season, recently revealed that the storyline between Sebastian and Blaine is "going less in a flirtatious direction" in upcoming episodes.
Glee returns with a new instalment on January 17 on Fox.