The 20-year-old midfielder has been called up to Australia's senior squad for the first time as they take on the Republic of Ireland in a friendly in Limerick on Wednesday.
Striker Barry Hayles, who replaced Bozanic on Saturday before going on to grab the winner in the 2-1 triumph over Grimsby, could also be set to miss out as he is on jury service.
The former Bristol Rovers, Fulham and Plymouth marksman was absent from training last week due to his involvement in London and he is set to find out whether or not it will prevent him from taking to the pitch on Tuesday night.
Defender Michael Townsend has battled with a knee injury of late but was named on the bench against the Mariners, and he should be competing for a place in Allen's matchday squad once again.
The Robins boss warned his players after Saturday's clash that they will have to up their game the visit of Southend. He told the club's official website: "I told them to get ready from the very first minute, to be competitive, to want the ball and pass it more and play better, quicker football. A team from the league above is here, so let's bring them here and beat them so we can get through to the second round."