Pato's injury problems are a concern for Milan vice-president Adriano Galliani and he is now on trial to prove his class leading up to the summer market.
Milan media sources say the Brazilian is no longer 'unsaleable' and is effectively on trial for the remainder of this season. If his consistency doesn't improve, the Rossoneri will be prepared to sell - and even his relationship with director Barbara Berlusconi will not save him.
Pato's availability will spark a rush from Europe's biggest clubs. Chelsea owner Roman Abramovich is a big fan of the youngster, as is his manager Andre Villas-Boas.
Barca coach Pep Guardiola was impressed by Pato in their Champions League clash earlier this season and can see him fitting seamlessly into his playing system.