Sergison Bates' 1998 Wharf Bar pub in Walsall is set to face the wrecking ball if Alsop's proposals, drawn up for Urban Splash, come to their full fruition.
The building, which is adjacent to Caruso St John's New Walsall Art Gallery, was critically acclaimed when it opened - to this day architecture students make international trips to visit it.
The practice credits it with launching it onto the international scene, which culminated in a joint professorship at Zurich University.
But Alsop describes the building as 'horrible'. 'I don't like it at all,' he said. 'It's not up to much.
'Also, it's falling apart,' he added. 'It wasn't built well and this needs to be done. It won't happen in the first phase but it will happen eventually.'
Alsop's plans would see the demolition of a whole swathe of Walsall and the construction of a series of new buildings by Alsop himself, Shed KM and rising Austrian stars Querkraft.
Urban Splash was more reticent about condemning the Sergison Bates building outright. 'We are in a dialogue with the owner of the long-lease of the bar about its future,' local director Nathan Cornish said.
'Our thinking is that the Gallery Square does not work very well at bringing people into the waterside site. We believe another public building such as a hotel might work better there.
'But if we can't come to an agreement with the landowner then we'll have to complete our scheme with the bar in place - the masterplan works with or without the pub.
'This is not about architectural merit - I really like it as a building. But the point is that we might get 15 or 20 better buildings if it goes and that must be remembered,' Cornish added.
The news of Urban Splash's potential plans were greeted with horror by the Twentieth Century Society. 'I think the Caruso St John gallery and the bar work really well together,' caseworker Cordula Zeidler told the AJ.
'The two architects naturally complement each other and it seems a real shame to take one of the buildings away. It would be a real waste of a really good building.' she said.
Responding to Alsop's comments about the pub, Stephen Bates, a founding partner of Sergison Bates, referred to its CAMRA award for 'best new pub of the year' in 1999.
'I am not that interested in his opinions on architecture,' he said of Alsop. 'But we would be sad and disappointed to see the pub go.
'This also forms part of an interesting debate about the demolition of relatively new buildings,' he added.