The 31-year old Swedish midfielder, of Japanese descent, joined the MLS club from IF Elfsborg in January and has since made four appearances in total for the 2011 and 2012 champions.
Ishizaki has featured in two MLS outings against Real Salt Lake and two CONCACAF Champions League clashes with Club Tijuana and Arena was looking for him to make an impact as soon as he adapts to the competition.
"It takes time for any player coming into the league," said Arena.
"So on top of everything else - getting him fit again - he's got to get accustomed to the league and our team.
"There's a learning curve there. He's just working his way through that, and I think that's the case all the time [with players]. You very rarely see someone who steps in right away and is fully adjusted. It takes time."
Arena added: "He's getting there. He's still a little bit away, but he's getting there. He's a good player. He's an experienced guy."
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