The midfielder was stretchered off ten minutes from time during Boxing Day's clash with his former club Tottenham.
The tackle with former team-mate Mauricio Taricco has resulted in Sherwood suffering a double fracture which will in all probability keep him on the sidelines until the summer.
"We won't see him again this season which is a blow for us," Pompey boss Harry Redknapp told Sky Sports News. "It is a big blow for us."
Redknapp will look to bolster his squad in January, as he added: "We need to get a couple in, whether it is loans or frees, and we need to get some bodies in to give us a squad.
"If we get a few injuries we are thin on the ground."
Sherwood will not require surgery and Pompey physio Gary Sadler added: "We have a fitness plan for Tim but he is likely to be ruled out for this season."
In other news, Redknapp is believed to have given the green light for defender Lewis Buxton to spend the rest of the season on loan at Bournemouth.
Cherries boss Sean O'Driscoll has been pleased with the 20-year-old and expects the loan extension to be completed next week.
