Reading midfielder Araon Tshibola has been ruled out for at least a month with an ankle injury.
The 20-year-old has made 15 appearances in all competitions this season.
"We're waiting on the specialist's report, but it doesn't look good for a number of weeks for Aaron," manager Steve Clarke told BBC Radio Berkshire.
"It's terrible news for Aaron and also a big blow for the squad because he's been a key member so far this season."
Midfielder Stephen Quinn and striker Hal Robson-Kanu will also miss Saturday's visit from Championship leaders Brighton.