The Dutch midfielder, on loan at the Liberty Stadium for a second season, suffered a head injury while training with the Netherlands squad and will be unavailable on Saturday
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A statement on the club's office website read: "De Guzman will be sidelined for the next seven to 10 days, meaning he is unavailable for Saturday's curtain-raiser against defending champions Manchester United at the Liberty Stadium.
"The 25-year-old could also miss [August 22's] Europa League play-off first leg against Romanian side Petrolul Ploiesti on home soil."
De Guzman was a key figure under Michael Laudrup last season, scoring eight times in 45 games as he convinced the Dane to renew his loan from Villarreal.
The midfielder featured in both legs of his side's 4-0 aggregate victory over Malmo in the Europa League, helping them to earn a play-off spot in their return to European football after 22 years.