Frank Lampard will leave Chelsea this summer unless he is given the five-year, £140,000-a-week contract that the England midfield player believes he deserves.

The London club have offered Lampard £140,000 a week in a four-year deal that is worth more than £29 million, but the 30-year-old is so disillusioned with his employers’ reluctance to bend to his will that he has decided to follow José Mourinho to Inter Milan before the transfer window closes at the end of next month.

The Italian club are confident that Lampard will be playing for them next season, despite Chelsea saying yesterday that they would not release him until his contract runs out next summer. Mourinho has persuaded Inter to offer Lampard a four-year deal worth £120,000 a week, which will become five years if Inter lift the European Cup while Lampard is at the club.

Lampard feels so strongly about Chelsea’s refusal to match Inter’s offer of an extra year that he is preparing to turn his back on the club and move his family to Milan. Chelsea have rejected Inter’s £8 million offer for a player who has scored 110 goals and won two league titles since he arrived at the club from West Ham United in 2001, but they are likely to soften their stance when they discover that his heart is no longer at Stamford Bridge.

“We have offered him what we believe to be a very good new contract,” Bruce Buck, the Chelsea chairman, said. “He has, for the moment, decided not to accept that contract. Having said that, there is still one year remaining on his contract and we expect and hope that he will honour it. During the course of the year there will still be the opportunity to sign the new contract because the offer that we have made remains on the table.”

Inter will ignore Buck’s claim that Lampard is not for sale and submit an offer of £10 million. The Italian champions wrote to Chelsea on Monday to ask if they could discuss buying Lampard but, despite being told that he was not for sale, they submitted an £8 million cash offer on Tuesday. “I know that the possibility of Lampard is still open,” Beppe Baresi, the Inter assistant coach, said yesterday.

According to Buck, Chelsea are expecting to sell about six players and bring in one or two this summer, but they have denied reports in Spain that they are close to signing Robinho, the Brazil forward, from Real Madrid. Spanish newspapers claimed last night that Robinho’s agent had arrived in London to negotiate a £28 million transfer, but this has been dismissed.

One player Chelsea are happy to sell is Steve Sidwell, who has agreed to join Aston Villa in a £5 million deal. The former Reading midfield player arrived on a free transfer a year ago.