The 20-year-old has been training with the Premier League leaders since the middle of January, with the blessing of the Championship club.
Red Devils boss Sir Alex Ferguson was keen to take a closer look at the Ghana international, with a view to bringing him to Old Trafford on a permanent basis, and has now agreed with Foxes boss Nigel Pearson to keep Schlupp at Carrington until the end of the month.
"He's stayed there, we've agreed to extend that," confirmed Pearson in an interview with Press Association Sport.
"I have spoken to him a few times and Jeff is enjoying himself there, things are going well. I think it's great experience for the lad."
Schlupp came through the youth ranks at Leicester, exploding onto the first-team scene following a successful spell with Brentford in 2011, where he scored six goals in ten appearances for the League One outfit.
The African has struggled with injury over the past 18 months, and has played only five times for the promotion hopefuls this campaign, the majority of which have been at left-back, as cover for the injured Paul Konchesky.
However, at Manchester United, Schlupp is catching the eye of Ferguson and his coaches, and could yet earn himself a lucrative move in the future.