Officials announced the 145-pound title fight on Tuesday. Freire is a two-time featherweight champion and will be seeking his first defense since he reclaimed the belt in April 2017.
The two have met previously, at Bellator 138 in June 2015. Freire won the first meeting via second-round knockout. They were supposed to meet in November, but Freire was forced to withdraw from a scheduled rematch thanks to injuries.
Freire (26-4) explored the possibility of a lightweight fight against former champion Michael Chandler earlier this year, but the fight didn't come together.
Weichel (39-9), of Germany, is on a four-fight win streak.