The Red Devils yesterday agreed a £75m deal for the Everton striker.
Starsport understand the Belgium international has given the green light to a long-term contract at Old Trafford worth £250,000-a-week.
United are putting Lukaku through a medical in Los Angeles.
But, according to the Telegraph, Chelsea have made a dramatic intervention at the 11th hour.
The Premier League champions were confident of sealing a deal for Lukaku before United trumped them.
Lukaku now faces a decision between the two clubs.
But the Telegraph report that Chelsea are unwilling to pay the agent fees to Mino Raiola that United are happy to cough up.
Stamford Bridge bosses believe Lukaku favours a return to the club.
Lukaku failed to make the grade in SW6 before being sold to Everton for £28m in 2014.
The 24-year-old is currently on holiday in LA with United midfielder Paul Pogba.
