The 27-year-old has endured a difficult first season in Spain, following his £33million move to the Santiago Bernabeu, and could be open to a return to the Premier League.
Red Devils boss Sir Alex Ferguson wanted to bring the former Tottenham Hotspur midfielder to Old Trafford before he signed for Real Madrid, and is ready to reignite interest in the Croatian international when the transfer window reopens on July 1.
Modric is understood to have told friends he would welcome the opportunity to move back to England after struggling to establish himself in Jose Mourinho's side.
He came off the substitutes' bench to inspire Real Madrid to their Champions League last-16 second leg victory over Manchester United last week, scoring only his second goal for the Primera Division giants in what has been a largely underwhelming debut campaign for Los Blancos.
Chelsea have also been alerted to Modric's potential availability, and will rival Manchester United for his signature as Roman Abramovich looks to finally lure him to Stamford Bridge.
However, Ferguson is reportedly confident he is in pole position if Real Madrid agree to sell at the end of the season.