The former Tottenham Hotspur midfielder has failed to make much of an impact since joining Real Madrid in the summer and was voted the worst signing of the season in La Liga this month.
Chelsea had a £40million bid rejected by Spurs for the Croatian midfielder in 2011 but are set to offer Madrid £22million in the summer to tempt the attacking midfielder back to the Premier League.
Jose Mourinho has been rumoured to be on his way out of Madrid at the end of this season and that would leave Modric in a tough position with such high competition for his position and a new manager to impress.
Spurs were understandably adamant that they would not sell to rivals Chelsea, but if Modric continues to struggle in Spain then a move back to London may well be viable in the summer.
Chelsea see Modric as the long term replacement of the outgoing Frank Lampard.