O'Connell has suffered a setback in his recovery from knee surgery, while Norwegian international Berge also went under the knife to correct a hamstring issue he suffered against Manchester United.
And Wilder, speaking ahead of Monday's trip to West Ham United, said: "Jack's had a couple of issues which we knew would be the case, and Sander's working extremely hard.
"They've both got brilliant attitudes and want to be out there, fighting for their teammates. But it's dictated by the medical department and people more qualified than me, if it was me I'd get them out there.
"They're not there just yet, but they'll be welcomed straight into a group who knows how important those two players are."
United could be boosted by the return of two key men for the trip to London, with full-backs George Baldock and Enda Stevens approaching fitness again after their respective injury worries.
"Enda has worked this week and George trained as well, so if he comes through today [Saturday] then he'll be on the train down to London," Wilder confirmed.
If Baldock is passed fit, it will give Wilder an interesting selection headache at right-back considering the impressive recent form of Jayden Bogle, following his summer move from Derby County.
Max Lowe, who also arrived at Bramall Lane in a double deal with Bogle, is currently in possession of the left-back slot.