The couple had a brief relationship earlier in the season but broke up because of the feelings Rachel had for Finn (Cory Monteith).
However, Falchuk told Zap2It that the duo will reunite in a future episode.
"They'll have a couple of steamy scenes," he said. "That's a relationship [where it's] sort of hard to keep those two apart. They're a little bit, like, hot and cold and it's so fun to see them together. Especially the actors, Mark and Lea, they're just great together."
Glee continues Tuesdays at 9pm on Fox in the US and Mondays at 9pm on E4 in the UK.