Brighton and Hove Albion have completed two midfield loan signings ahead of the transfer deadline.
O'Callaghan has made 12 appearances for Ipswich
Ipswich's George O'Callaghan, 27, and Le Havre's David Martot, 26, go straight into the squad for the home game with Southend United.
Manager Dean Wilkins told BBC SCR: "Martot's a mobile midfield player who can do a bit of everything.
"George is a strong character who will take responsibility and we are hoping he will bring a rhythm to our game."
O'Callaghan turned down the offer of a permanent move to the League One club after failing to agree personal terms.
Former Port Vale man O'Callaghan moved to Portman Road from Cork City in January for an undisclosed fee and has made 12 first-team appearances, scoring one goal.
Meanwhile, Martot has impressed during his spell on trial with Brighton this week.
Ipswich failed with a bid for Spanish defender Cesar Navas, 27, after they agreed a fee with Malaga but he opted to stay in his homeland.