"We were training," Nolan said. "We didn't know who we were playing until we'd finished and Gary Speed got a text message.
"It looked like they were from Russia on the text, then we saw they were from Bulgaria.
"We'll find out more about them over the next couple of weeks," Nolan said. "It looks like it might be a tough one but, hopefully, we'll be OK.
"We've got to be happy with the draw - in fact we're just happy to be in it.
"Maybe we'll sit round the telly when they make the draw for the semis."
Stelios, who was a Champions League regular with Olympiakos, knows enough about Bulgarian football to know Wanderers will need a good lead from the home leg if they are to avoid any slip-ups in the return.
"I haven't played there but I have been to Bulgaria for a couple of pre-seasons," he said. "I know it's a poor country and it's not the easiest of places to play football, so we will need a good result from the first game so that we have no nerves when we go there."