The most experience he had was with Sheffield United, playing 33 games for Chris Wilder in 2017/2018.
Blackman will be hoping to impress enough at Rotherham to earn a permanent move somewhere next summer.
| Welcome to Rotherham United, Jamal Blackman!
The Chelsea stopper arrives on a season-long loan at AESSEAL New York Stadium, subject to PL, EFL and FA ratification.#rufc | #ForeverTogetherForeverProudpic.twitter.com/hGPN8MTJ3F
— Rotherham United (@OfficialRUFC) August 24, 2020