The 27-year old Argentine playmaker has provided just two assists and is goal-less in nine league matches since his offseason arrival in Philly, failing to play out a full 90 minutes for the Union.
"Cristian, first and foremost, has to adapt to the level of fitness of the players in this league," Hackworth said during his weekly press conference Tuesday.
"There's a reason why he hasn't gone 90. And we've been working on his fitness since he arrived. That has been an issue."
He added: "I think people have to be patient with a player who comes from a very different culture and is trying to adapt to this league.
"It's a big challenge, and there's a long list of players that were extremely successful coming in from other leagues around the world that struggled [at first].
"He's a guy we believe in and certainly we'll see a lot more of - but he has areas of his game that have to improve."
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