West Ham United FC (@whufc_official) September 2, 2015
Both players left Championship clubs, Jelavic leaving Hull City, and Antonio departing Nottingham Forest, to sign permanent deals with the Hammers.
There is no game this weekend due to the international break, giving both players a chance to get acclimatised in east London and get to know their teammates.
Jelavic has experience in the Premier League, netting 29 goals in 101 games in the division for Everton and Hull City.
Antonio struck 15 goals in all competitions for Nottingham Forest last season, having signed from Sheffield Wednesday.
West Ham's next game is a home fixture against Newcastle United on September 14, who are currently four points behind them in the table at this early stage.
Both players will be doing all they can to impress to get in with a chance of featuring, along with loanees Alex Song and Victor Moses who also clinched deadline day moves.