The 20-year-old striker broke his foot during Manchester United's 3-0 defeat against Premiership reining champions Chelsea on Saturday and will be out for at least six weeks.
"I knew yesterday (Tuesday) that he had more than one fracture, I don't know what that means but I'm not pessimistic," Eriksson was quoted as saying by Sky Sports Network.
"Maybe he needs a miracle, miracles happen in life every now and then, I don't really know."
An initial scan showed that he broke one bone but further medical exams proofed that more bones were damaged.
Rooney will have his final examination on Thursday morning when it will be confirmed whether he will be able to take part in Germany or not.
The Swede stressed that he will name Rooney in the squad to be announced on Monday and set to include 26 players.
"I will not rule him out until the doctors tell me there's no chance, no one wants that to happen, everyone hopes he can take part in the World Cup at some stage," Eriksson said.
FIFA said earlier this week that England will be able to replace Rooney until 24 hours before their World Cup opener against Paraguay on June 10th, should they provide a medical report to prove a serious injury.
England play in Group B that also includes Sweden and Trinidad and Tobago.