Real Madrid 's efforts to sign Neymar may hinge on a transfer demand made by Paris Saint-Germain as part of any deal for the Brazilian.
The 27-year-old is widely expected to leave France in the summer after two years at Parc des Princes following his world-record transfer from Barcelona in 2017.
A return to Barca has been suggested, as has a move to their La Liga rivals Real.
PSG, who paid €220m to secure Neymar's signature, are said to be unwilling to consider letting the Brazilian go for less than what they forked out for his two summers ago.
However, the French club have offered Real a chance to sign the forward for less than that - as long as they add one of his countrymen to the deal.
Marca report that the Ligue 1 champions want Casemiro to be involved in any transfer that would take fellow Brazilian Neymar to the Spanish capital.
It remains to be seen whether that is something the La Liga heavyweights would consider with the defensive midfielder a key figure under boss Zinedine Zidane.
In the Frenchman's first spell in charge of Los Galacticos, the 27-year-old anchored the midfield as Real won three successive Champions League titles from 2016-2018.
With Zidane planning a summer overhaul of both playing staff and style after a disappointing season both domestically and in Europe for Real, Casemiro may no longer find himself as a guaranteed starter.
The seemingly inevitable arrival of Manchester United midfielder Paul Pogba in the Spanish capital may also put the Brazilian's position under threat.
PSG have tracked Casemiro for some time and it is thought the French champions view him as the ideal player to plug the gap left by Thiago Motta's retirement last season.
And if Casemiro were to be added to a deal involving Neymar, it would drastically reduce the layout Real would have to consider.
