On 30 July 2014, Brüls signed for another Ligue 1 side, joining Rennes on a three–year contract.
It wasn't until on 6 October 2014 when Brüls was given number thirteen shirt.

Brüls suffered a foot injury at the start of the season and was sidelined for three months.
In November 2014, Brüls recovered from a foot injury and made his full return to training.
It wasn't until on 29 November 2014 when Brüls made his Stade Rennais debut, coming on as a substitute in the second half, in a 2–0 win over Monaco.
In the next game against Nice on 3 December 2014, Brüls set up a goal for Anders Konradsen, in a 2–1 win for Stade Rennais.
However, Brüls' first season at Stade Rennais was restricted to twelve appearance in all competitions.

However, ahead of the 2015–16 season, Brüls' first-team opportunities was expected to be limited after Philippe Montanier told him he won't be featured in his plan.
Following his loan spell at Standard Liège came to an end, Brüls said he's uncertain on his future at Stade Rennais whether or not he would play for the club next season.
On 30 July 2014, Brüls signed for another Ligue 1 side, joining Rennes on a three–year contract. It wasn't until on 6 October 2014 when Brüls was given number thirteen shirt.
Brüls suffered a foot injury at the start of the season and was sidelined for three months. In November 2014, Brüls recovered from a foot injury and made his full return to training. It wasn't until on 29 November 2014 when Brüls made his Stade Rennais debut, coming on as a substitute in the second half, in a 2–0 win over Monaco. In the next game against Nice on 3 December 2014, Brüls set up a goal for Anders Konradsen, in a 2–1 win for Stade Rennais. However, Brüls' first season at Stade Rennais was restricted to twelve appearance in all competitions.
However, ahead of the 2015–16 season, Brüls' first-team opportunities was expected to be limited after Philippe Montanier told him he won't be featured in his plan. Following his loan spell at Standard Liège came to an end, Brüls said he's uncertain on his future at Stade Rennais whether or not he would play for the club next season.
Christian Brüls