The Sun says the former Chelsea boss was not due to return from a family break for another five days.
But Mourinho was back in Milan last night and told the club he will oversee the Lamps deal.
The Italian giants had a £6.6million offer rejected by Chelsea last week. But Mourinho is desperate to make the England midfielder his first major signing.
Chelsea have told Inter that no deal will be done for Lampard until Phil Scolari has assessed his squad.
The new manager is due to arrive in London tomorrow.