The Romania international has been strongly linked with a move to the Barclays Premier League, with Arsenal and Manchester City reportedly keen to acquire the 25-year-old's services.
"We are working with someone in England," Radu's agent Viktor Becali told lalaziosiamonoi.it. "There are three clubs that are very interested in Stefan.
"If we were to receive a good offer and Lazio were to accept, then he could leave.
"Otherwise, he is happy to remain in Rome. He is under contract until 2016."
Radu joined Lazio from Dinamo Bucharest in 2008 and made 21 Serie A appareances for the Biancoceleste in the 2011/12 season.