With Christian Bruls arriving from Gent on Wednesday, Rennes further bolstered their midfield options on Thursday by completing the signing of Bosnia Under-21 international Prcic.
The 20-year-old made his breakthrough at Sochaux last season, making in 29 league outings, 20 of which were starts.
He was unable to save the club from relegation to Ligue 2, but his performances earned him a move to Rennes and another chance to impress in the top flight.
"I am very happy to sign for the club," he told Rennes' official website. "Everyone has welcomed me very well.
"It's the start of a new stage for me. I had never left my family and friends and it is a bit strange, but I am happy. I needed to take this step.
"Everything is in place here for me to progress and develop. Stade Rennais have always been a very good club and are capable of playing in Europe.
"The competition [for places] helps people perform above themselves. When you have lots of players for the same position, you want to show to the coach that you deserve a place in the team.
"I am a box-to-box player but at heart, I am more attacking and quite comfortable with the ball at my feet."