Italy midfielder Daniele De Rossi looks unlikely to face Germany in Saturday's Euro 2016 quarter-final because of a bruised thigh.
"He is working very hard, we are doing everything for him to recover and we can't give a timeframe but we are aware that the problem is serious," he said.
Midfielder Antonio Candreva's groin strain has also not recovered enough for him to return, the team doctor said.
"Candreva has tried to recover in every possible way, working very hard," said Castellacci.
"There has been a significant improvement but not enough for him to be reintroduced into the team."
De Rossi's absence would be a blow for coach Antonio Conte with Thiago Motta, his most likely replacement, also missing through suspension.
Veteran De Rossi was used sparingly in the qualifiers but he has been back in favour during the tournament, proving himself to be an important figure for Italy.
Image: Italy's Daniele De Rossi signs autographs in Montpellier, France, on Wednesday
Photograph: Claudio Villa/Getty Images
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