The FC Dallas winger has recently been linked with a January move to the Liberty Stadium, but it now looks he could be heading to Mexico instead.
According to ESPN.com.mx, Mexican giants Club America are in discussions to sign the Colombia international this winter ahead of the 2016 Clausura campaign and could spend as much as $7.5 million [£4.94 million] to bring him on board.
The report adds that Swansea were looking at the MLS hotshot last month, when The Sun even suggested that the Premier League side had lodged a £4 million bid for his signature, but it now remains to be seen how these latest developments will affect their alleged interest.
Castillo, 23, originally joined Dallas from boyhood club Deportivo Cali in March 2011 and has since scored 29 goals in 135 MLS regular season appearances, while adding 24 assists.
Arguably the league’s fastest player, the skilful wide man enjoyed a breakout 2014 season and has taken another big step forward this term, recording 10 goals and a career-high nine assists in 32 league games to help Oscar Pareja’s fledgling side make the Western Conference final.
As well as earning a first MLS All-Star Game appearance against Tottenham Hotspur in the summer, his impressive performances have also seen him break into the Colombia national team in recent months, and there now appears to be growing interest in his services with just under six weeks to go before the winter transfer window opens.
Having signed a new five-year deal until 2019 in February, Dallas club president Dan Hunt stressed last month that the team have no desire to sell their star man, but Castillo himself is said to be open to exploring his options.
Comparable to Swansea’s own South American winger, Jefferson Montero, the three-time capped attacker certainly has both the physical and technical ability to succeed in the English top-flight, but it sounds like he could be heading to Liga MX instead if the Welsh outfit do not move fast.