Milan's famous footballing rivals – Internazionale Milano and AC Milan – will have to go back to the drawing board and reconsider their joint plans for a new stadium.

In September, the clubs announced that two teams of architects – Populous and Manica/Sportium – had been shortlisted to design a new 60,000-seat stadium at the site of the current San Siro stadium.

The proposals are based on demolishing the current venue and replacing it with an entirely new stadium and an entertainment district.

The ambitious plans were seen as a breakthrough and came after years of the clubs planning to either replace the historic, but ageing, San Siro – or move away from it into two new, separate stadiums.

The latest plans, however, have now been cast in doubt after a Milan City Council planning decision.

While the council voted in favour for the San Siro to be regenerated, it called the latest plans "unacceptable" and "excessive in size" – and added no less than 16 clauses to the approval.

Among the conditions is one which seems to dismiss the current plans – a stipulation that the existing stadium "must be retained" in some way or another.

In practice, this means that the clubs will now have to look at either regenerating the existing San Siro or finding enough space to leave it standing and build the new venue next to it.

San Siro first opened in 1926 and for the 21 years was the home of AC Milan. Inter Milan moved in in 1947 and the fierce rivals have shared the venue ever since.