Heavy rainfall last month saw the nearly 18in deep ground at the Hard Interchange reduced to ‘grey sludge’ – worsening the problem with the ground sinking.
Portsmouth City Council has previously said it is not in a legal dispute with its contractor Osborne and designer RoC Consulting.
But now the authority has confirmed it is in ‘legal processes with the designer and contractor’.
As reported, the ground has been sinking, sparking a major replacement plan at the area where buses wait for passengers.
Temporary repairs for the longstanding problem, made worse by the rain, were completed at the end of last month.
But that was little comfort for support worker Victor Childs whose disabled client nearly lost his shoe walking in the sludge-like substance.
The 74-year-old from Southsea, was with the client on a day out when he inadvertently stepped on what should have been hard ground.
‘It was liquid,’ Mr Childs said. ‘The client has got black shoes on which turned grey. I was lucky, I happened to be wearing grey trousers.
‘It was coming out of the bus interchange but it was right across the whole thing. I didn’t realise it was so deep - it was about two inches thick.
‘It looked like grey sludge. It was quite disgusting really.
‘The thing that was there before was perfectly adequate. There was the best cafe in Portsmouth and views across the harbour.
‘They’ve spent millions of pounds and what have we got? It’s a mess.’
The design award-winning site has cost the council thousands to fill in potholes at the bus apron, the area where buses wait, since it opened in March 2017.
A city council spokeswoman apologised for the latest problem and said: ‘Our goal is still to replace the surface completely, so it can withstand wear and tear for many years, but first we need to complete legal processes with the designer and contractor.’
But she added: ‘We are continuing with the process of discussions and negotiations with both the designer and construction company. We remain hopeful that we can resolve this matter, without the need for litigation.’
A spokesman for contractor Osborne said: ‘We are supporting Portsmouth City Council to seek a resolution and therefore it would not be appropriate to comment further at this time.’
The firm did not respond after being asked for more detail.
RoC Consulting, based in Manchester, declined to comment.