The South Korea midfielder missed training on Tuesday with a virus and he will not be available for the visit of the Bundesliga champions.
Patrice Evra also came down with the illness over the weekend, but the Frenchman has recovered in time to take his place in the squad.
Michael Owen sat out training on Tuesday with a groin problem, although he is expected to shake it off in time to be named in Sir Alex Ferguson's squad.
"Ji-sung has a virus," said Ferguson. "Patrice Evra had it at the weekend. After the Stoke game he felt a bit uneasy - he was in bed on Sunday and didn't come to training, but he came in for a bit yesterday, came in today [Tuesday] and he should be alright.
"Michael should be alright for tomorrow. He had a tight groin in training yesterday, nothing serious. But obviously for the game tomorrow we didn't want to be pushing that. Other than that, everyone's fit."
United (from): Foster, Kuszczak, Neville, O'Shea, Brown, Ferdinand, Vidic, Evans, Evra, Fabio, Valencia, Anderson, Carrick, Fletcher, Gibson, Giggs, Nani, Rooney, Berbatov, Owen, Scholes.