Quagliarella has become one of the most in-demand strikers in Serie A since his move to Samp last summer, and the 23-year-old announced his potential to a wider audience with two stunning goals in Italy's recent Euro 2008 qualifier against Lithuania.
After scoring 13 goals in 35 league appearances for Samp last season, his agent has now opened the door to a possible move to England.
"One month ago, Manchester United made a £10million offer," said Pagliari
"We believe Fabio is worth between €15 to €20million (£10 to £13million), hence if the English club's offer still stands, he could probably go abroad."
United chief executive David Gill has previously hinted that the English champions are seeking to purchase a new striker after already reinforcing their squad with the additions of Owen Hargreaves, Nani and Anderson.