The teenager joined the Red Devils from FC Zurich in 2013 and spent most part of his time away from the Red Devils’ first team. He was part of United squad and made one senior appearance during their 4-0 defeat to MK Dons in the Capital One Cup last August.
Janko has joined Celtic on a permanent transfer and signed a new four-year contract.
“Saidy Janko is to sign for Celtic after agreeing a four-year contract with the Scottish Premier League champions,” a statement read on United’s official website.
“The Swiss right-back, who spent the end of last season on loan with Bolton Wanderers, is expected to finalise the move once routine medical results are received.