Chelsea have £13m buy-back option for Thorgan Hazard but clause expires at the end of the year

He was the forgotten brother at Stamford Bridge but Thorgan Hazard has since made a name for himself in Germany.

The younger sibling of Chelsea star Eden Hazard swapped west London for Borussia Monchengladbach on a permanent basis in February 2015 - after initially joining the latter on a season-long loan that 2014-15 term.

The 23-year-old didn't make a single appearance for the Blues during his three years at the club but Roman Abramovich was shrewd enough to insert a buy-back option upon his sale.

Chelsea have a £13million buy-back option on attacking midfielder Thorgan Hazard

The Blues' deal to re-sign the 23-year-old though expires on December 31, 2016

Hazard is the younger sibling of brother Eden - who is still at Stamford Bridge

According to Bild, Chelsea can re-sign the Belgium international for £13million - however, the clause expires on December 31, 2016.

Hazard has enjoyed a brilliant start to this season at Monchengladbach and his departure would be a major blow to their domestic and European aspirations.

Gladbach's No 10 was on the scoresheet during Wednesday night's 2-1 home defeat by Barcelona in the Champions League - a strike taking his tally to seven in 10 matches.

Hazard scored during Gladbach's 2-1 Champions League home defeat by Barcelona

In a statement on their website following the attacking midfielder's sale, Chelsea said they would 'continue to monitor his progress'.

However, Hazard has reassured Gladbach fans that his focus is simply with the German club.

'I've signed a long-term deal and I am only focused on Borussia,' he told Bild.

'I feel good here, and am currently not thinking about any other club.'