Saidy joined Manchester United in the summer of 2013 from FC Zurich. Having joined Manchester Unied as a right back, Janko has spent much of his debut season on the right wing for the U-21 team. His physical presence and speed saw comparisons made with Antonio Valencia.
Saidy made his first team debut away to MK Dons in the 2nd Round of the 2014/15 League Cup, he was substituted at half time.
At the start of February 2015, Saidy joined Bolton Wanderers on loan for the remainder of the 2014/15 season. He signed a four year contract with Celtic on the 1st July 2015.