The actress makes a special appearance as substitute teacher Holly Holiday in the musical TV drama and Matthew â who plays Will Schuester â admitted she worried about hurting him as they danced together.
He told website Access Hollywood: "We're doing the Argentine tango, so you're in-between their legs and you're kicking up and stuff."
Pointing to his inner thigh, he added: "So she's kicking in here, and she's like, 'I'm so scared that I'm going to hit your man-love!'
"And I said, 'You know, just go for it.' And she did and she connected a couple of times."
He added: "The episode is called 'Sexy' and Holly comes back as a sex-ed teacher and we teach the kids about sex through music."
He explained: "I'm not dating anyone. I don't feel like I'm in a good place to be a good boyfriend.
"I know how much work it is to be in a relationship and I don't have the time to put in that work right now."