“Negotiations are at an advanced stage and the situation is very interesting,” revealed agent Juan Carlos Padilla on mediotiempo.com.

“I knew there was the possibility this could happen and it is all becoming more and more real. Betis have the priority, as they were the first club to show an interest in Nery.

“Next week there will be a clarification over which side, between Betis and Roma, will be the future of the player.”

Castillo is a 24-year-old Mexican international who can play as a forward or on either flank.

“Even if Roma play in the Champions League, we have to consider what they will offer and whether Nery will be a key figure or not. The decision only depends on us, but we have to be wary: it is not an issue of money.”

Castillo played in Greece with Olympiakos for seven years, had a rough patch at Shakhtar Donetsk when he got into an argument with teammate Cristiano Lucarelli and moved to Manchester City on loan in December 2007.

However, he does not look set to stay for the entirety of the one-year deal due to the increased competition at Eastlands.