The Senegalese strained ligaments in his right knee while attempting to make a challenge in Pompey's Premier League loss at Emirates Stadium on December 28.

And after visiting a consultant, head physio Gary Sadler confirmed on Monday that the former Fulham enforcer will be out for a minimum of 12 weeks, with damage to Diop's posterior cruciate ligament a particular worry.

"We'll be taking him back to see the consultant in six weeks and then we'll know a little bit more about it then,'' Sadler told his club's official website.

"He's in a brace and he's having treatment trying to get some of the swelling down on his knee.''

There is better news elsewhere, though, with England right-back Glen Johnson continuing his rehabilitation from a bruised knee and twisted ankle to put himself in line for a potential return against Manchester City at the weekend.

Johnson returned to training alongside ankle injury victim Younes Kaboul last week, and with winger John Utaka also back on Monday, manager Tony Adams could have an extra trio of players to call upon for the Fratton Park clash.