With Chelsea goalkeeper Thibaut Courtois not willing to give any guarantees in regards to his future at the club, it seems that the Blues are already lining up a long-term replacement for the Belgian player. According to the Daily Mail, Chelsea have seen AC Milan goalkeeper Gianluigi Donnarumma as an alternative to Courtois in case he eventually leaves the Blues. The Mail claims that Chelsea will offer £30 million for Donnarumma.
The 17-year-old Italian goalkeeper has been a starter for Milan since October last year, accumulating 22 appearances for the Rossoneri this season. Donnarumma earned his place at the team over former Real Madrid goalkeeper Diego López, who had collected poor showings as Milan's main goalkeeper as well as a thigh injury that took him out of the pitch for one month.
Donnarumma's talent is quite clear, and he's certainly among the top goalkeeping prospects on the planet right now. That said, he definitely isn't in a place yet to be considered an immediate replacement for Courtois, who despite his poor performances this season, remains one of the best goalkeepers in the world. The AC Milan youngster would almost certainly need several seasons on loan before being ready for the Chelsea first team, much like Courtois himself required before replacing Petr Cech.
The best case scenario for Chelsea would be keeping Courtois and telling Real Madrid to shove off (which is almost certain to happen anyway), while still adding the young Italian at a somewhat reasonable price. That scenario would allow the Blues to watch Dommarumma's development while controlling his future, and give them a viable plan of action in several seasons should Courtois ever push for a move, and if that never comes to pass, they'd potentially have a very valuable asset on their hands anyway.