McClay also said he had asked his officials to reassess the benefits of TPP without the United States.
Some TPP provisions would apply to all countries including the US whether or not they were TPP parties, such as greater transparency around Pharmac decisions or extending copyright from 50 years to 70 years.
But some, such as market access and tariffs, would apply among the parties only.
He said the total annual tariff savings to New Zealand with the US in TPP had been estimated at $270 million and without the US had been modelled at $220 million.
"It is still significant savings for us - and that it is the first free trade agreement for us with Japan, Mexico, Peru and Canada."
By way of example, he said New Zealand beef exports to Japan currently faced a 38.5 per cent; Australia had an FTA with Japan and its tariff had fallen to about 27 per cent but under TPP the rate would fall to 9 per cent over time for TPP parties, including New Zealand and Australia but Japanese tariffs on US beef would remain at 38.5 per cent.
"It's important for New Zealand to be involved in agreement like TPP because it levels the playing field for our producers and exporters."
Without TPP, New Zealand would at a disadvantage to Australia and other nations that had a preferential trade agreement.
"When agreements go ahead without us, it erodes our competitiveness in markets because others have better tariff rates than we do."
US President Donald Trump withdrew the United States from TPP in his first week in office, in January.
The technical issues officials are thought to be considering include how to convert a 12-country agreement to an 11-country agreement; how the US might be able to join in the future and how other countries could join up.
McClay said there will be nothing to present to the New Zealand Parliament before the House rises on August 17 for the election on September 23.
He said he would be giving a briefing to Parliament's foreign affairs and trade committee on Thursday and he was happy to sit down with Labour trade spokesman David Parker to brief him further.
Labour, the Greens and New Zealand First oppose TPP.
McClay will be staying on in Vietnam for a meeting of an Asian regional trade deal being negotiated, the Regional Comprehensive Economic Partnership.
The 11 TPP countries are: New Zealand, Singapore, Brunei, Chile, Peru, Australia, Vietnam, Malaysia, Japan, Mexico, Canada.