Portsmouth manager Andy Awford has confirmed key central-defensive pair Jack Whatmough and Paul Robinson are out for the rest of the season.
Whatmough has knee ligament damage and will be out for several months while Robinson has had cheekbone surgery but will be available for next season.
"It's another blow," Awford told BBC Radio Solent. "To lose two centre-backs at this stage is a toughie."
Meanwhile, Josh Passley has extended his loan until the end of the season.
The 20-year-old Fulham defender has made nine appearances since arriving at Fratton Park in January.
Whatmough, 18, has played 24 times for Pompey this season and Awford says he will be a huge loss.
"It looks like it's going to be months rather than weeks with his injury, but he is young, strong and mentally-equipped," said Awford. "He has a good team behind him that will look to get him back out there as soon as possible."
Robinson joined on loan from Millwall in August and made the move permanent in January. He has played 38 times for the League Two club this season.
"He had an operation on Monday to his cheekbone and I'm almost 95% certain he won't play again this season," added the Portsmouth boss.