Rafael Benitez's men had inserted a January recall clause in the terms of the striker's deal with West Brom, but that option expired on Monday.

It means Lukaku will remain at the Hawthorns until the off-season, as he looks to build on the impressive form which has seen him net seven times in 21 appearances.

The 19-year-old helped Steve Clarke's side get off to a blistering start to the season, and they sit seventh in the English Premier League despite a recent dip in form.

The Belgian is set to face tough competition upon his eventual return to Stamford Bridge, with Chelsea having recently purchased striker Demba Ba to battle with Fernando Torres for a starting berth.