Peszko suffered the injury in Wolves' 2-1 defeat to Crystal Palace on Tuesday night and Solbakken has admitted that it is a big blow to the club.
Solbakken told BBC WM: "It's not good news. His ligament is stretched. He will be out for a long time."
The injury to Peszko comes just three days after fellow winger Razak Boukari suffered a calf problem in Wolves' win over Sheffield Wednesday at the weekend.