The former Newcastle striker, 26, was jailed for eight months in May after admitting online banking fraud.
Southend boss Phil Brown expects Ranger to return to training before their first League One game on 5 August.
"When the season starts, we'll try to get games behind closed doors so he can get a level of match fitness," Brown told BBC Essex.
After Ranger pleaded guilty to conspiracy to defraud by obtaining bank details and transferring money, Southend said they would consider the player's future.
Speaking after their pre-season friendly defeat by Brighton on Tuesday, Brown said: "Nile has to understand that these players are playing with discipline and have done for the last three or four weeks.
"The best we will get out of Nile is probably a week's work and that won't be enough for him to be fit for the [start of the] season."
Ranger joined Southend in August 2016 and scored eight goals in 27 league appearances last season.
Southend United will give striker Nile Ranger a chance to relaunch his career when he is released from prison.