The midfielder was felled following a crunching tackle from his former Spurs team-mate Mauricio Taricco and received lengthy medical treatment on the pitch before being stretchered off to hospital where he was to undergo X-rays.
Sherwood is now out of Sunday's Premiership clash with Chelsea and could be facing a lengthy spell on the sidelines if manager Harry Redknapp's worst fears are confirmed, making him the fourth central midfielder currently in Pompey's treatment room.
"Tim Sherwood is the type of player you want on your team and he was having another good game today," said his manager.
"His injury looks bad - he isn't in a good shape. He can't walk and it could be a broken leg."
The tackle was accompanied by a loud crack but Redknapp refused to criticise Taricco and said: "I heard something but it didn't look like a bad challenge from Taricco. I didn't have a clear view so I don't want to say too much."