Manchester United wanted to sign Kroos during his time at Bayern Munich back in 2014.
However, the sacking of David Moyes and appointment of Louis van Gaal ultimately scuppered a deal.
Kroos has gone on to shine for Madrid and helped the Spanish giants win the Champions League last season.
And the Independent claim the German midfielder is back on United's radar.
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Toni Kroos is back on Manchester United's radar, according to reports
David Moyes wanted to sign Toni Kroos during his time in charge of Manchester United
Mourinho is set to bolster his squad at the end of the season with a long-term replacement for Michael Carrick on his agenda.
Carrick shone against Blackburn in the FA Cup yesterday but, the age of 35, United want reinforcements.
It is claimed United chiefs are prepared to make a summer bid to test Madrid's resolve.
Real Madrid retain an interest in Manchester United target Antoine Griezmann
And their bid to sign Kroos could be helped by Madrid's interest in Atletico Madrid striker Antoine Griezmann.
Though the France international is Mourinho's No1 summer target, Zinedine Zidane is also determined to sign him.
Should they poach the forward from their rivals it could spark an overhaul of the squad – and Kroos could move to United as a result.