Jack Whatmough has been ruled out through injury for six months.
The teenage defender suffered anterior cruciate ligament damage in Pompey’s 2-2 draw with Cheltenham last week.
A challenge from the Robins’ Shaun Harrad saw the Gosport youngster limp off in stoppage-time, with the Blues having used all three of their substitutes.
The injury represents a huge blow for the central defender, who has made 24 appearances for Andy Awford’s side this season.
More to follow.