The Millers completed the signing of Chelsea forward Izzy Brown on a season long loan in August 2016.
The 19-year-old has made one senior appearance for the Premier League giants after coming off the bench against former club West Bromwich Albion in 2015.
That was his second senior appearance in the top flight after becoming the second youngest player in the Premier League when he starred for West Brom in a home defeat to Wigan.
He joined Chelsea in 2013 and gained further experience last season after a loan spell in Holland with Vitesse Arnhem during the 2015/16 season.
The Peterborough-born ace has also represented England at under 16, 17 and 19 levels, and scored twice at AESSEAL New York Stadium for the 19s against Italy in a 3-0 victory in 2014.
He made his Rotherham debut in the home victory against Brentford.