Celtic have signed two Manchester City players under Brendan Rodgers.
Brendan Rodgers is likely to be in the market for new attacking talent this summer, after Roberts returned to City following his two and a half years north of the border. Charly Musonda has also cut short his 18-month loan from Chelsea.
Celtic need a playmaker that can play in the number 10 role and out wide, with Stuart Armstrong's future also in doubt as a handful of Premier League clubs reportedly circle.
Roberts and Ntcham have been huge successes since moving to Celtic, and that should tempt Rodgers into raiding City again - this time for West Ham target Diaz, who the Sun claim is interesting former City boss Manuel Pellegrini.
Making his debut for City in September 2016 under Guardiola, 18-year-old Diaz has since gone on to make 11 senior appearances for City - 10 of which came throughout the 2017-18 campaign.
He has also starred in City's Under-23 side, scoring six goals and adding four assists in 13 Premier League 2 games and four UEFA Youth League outings.
The Spain Under-19 international boasts huge technical ability, whether that be from out wide or in the middle of a three and has been likened to Barcelona's Lionel Messi by City Under-18 star Ed Francis in an interview with Goal.
Diaz would be the perfect replacement for Roberts, helping Celtic in their bid to achieve a third successive treble and reach the knockout stages of the Champions League.