Centre-half Fonte missed Wednesday night's 2-1 FA Cup replay win over Leicester through suspension and should come straight back in with Clint Hill reverting to left-back.
Oster is fit again following a calf injury and fellow midfielder Watson is also back in full training after his calf problem, although he may not be risked from the start.
Teenage forward Victor Moses looks set to miss out after limping off with an ankle injury against Leicester.
Fellow youngster Sean Scannell came on in place of Moses and grabbed Palace's second goal, so he could be in line for a start.
Defender Paddy McCarthy is out for three months after undergoing shoulder surgery.
Ipswich boss Jim Magilton is facing a defensive dilemma ahead of the trip to Crystal Palace.
On-loan Fulham defender Moritz Volz was set to start at right-back at Selhurst Park as contract rebel Alex Bruce moved across to centre-back as cover for the injured Ivan Campo.
But Volz has now picked up a groin injury and faces a late fitness test ahead of kick-off.
Campo had enjoyed a fine run of form alongside Gareth McAuley following his surprise recall against Birmingham on Boxing Day but tore a calf muscle against Sheffield Wednesday last Saturday and is starting a three-week lay-off.
Bruce is one of 14 players out of contract in the summer at Portman Road but has rejected the club's offer of a two-year deal. Any thoughts manager Jim Magilton may have had of leaving him out as a result seem to have been quashed by the decision to allow another centre-half - Richard Naylor - to join Leeds on loan.
Another defender David Wright remains out with a hamstring injury as Magilton looks for an away win to bolster Town's fading play-off hopes.Sporting Life