The forward sealed his Old Trafford departure in the final hours on deadline day after being left out of United's squad for their first two Premier League games.
Sancho, 24, will join the Blues on a permanent basis next summer for a fee worth around £23million, as revealed yesterday by Mail Sport.
But this obligation will not apply should Enzo Maresca's side fail to finish in the top 14 of the top-flight at the end of the current campaign, The Telegraph claim.
The final fee is also dependent on performance-related add-ons.
Jadon Sancho could return to Manchester United due to a clause in his loan move to Chelsea
United are initially said to have wanted around £40m for Sancho but ultimately wrapped up negotiations with Chelsea before the window slammed shut.
Juventus dropped out of the race after being unwilling to stump up the Red Devils' demands and the Blues subsequently swooped to snap up a replacement for Raheem Sterling.
Speaking as late as deadline day, Ten Hag had claimed that Sancho would stay at United.
'We need a good squad. We have to play many games until January. After the [international] break we play every third day so we need options.'
Sancho was frozen out at United following a public row with boss Ten Hag and spent the latter part of last season on loan at Bundesliga side Borussia Dortmund.
It appeared he had been handed a route back in to the first-team after his return to United this summer but Ten Hag chose not to select him despite clear the air talks.
Mail Sport previously reported that United and Chelsea had held surprise discussions over a swap deal involving Sancho and Sterling.
Sterling had been demoted to the 'bomb squad' at Stamford Bridge and told he would not play under Maresca - but a move to United did not materalise.