A versatile operator, Warren is in his third year as a professional after graduating through the Rotherham academy.
He signed a contract extension at the end of the 2016/17 season to remain at AESSEAL New York Stadium.
During 2015/16 he enjoyed a loan spell at Sheffield FC amd Harrogate Town, and was on the bench for the Millers for the Emirates FA Cup Third Round tie against Leeds United at Elland Road.
He made his professional debut for the Millers in a Carabao Cup tie against Morecambe in 2016, and was a regular in the matchday squad throughout the season.
The 20-year-old had loan spells earlier this season with Trinity`s league rivals Boston United and North Ferriby United, where his time was split, having been recalled ahead of the Millers’ trip to Bradford City in the Checkatrade Trophy.