Key took issue with Groser's comments to BusinessDesk last week that there was so far no deal on dairy products.
"It's not to say that there's a bad deal on dairy products, it's more to say that there's no deal," Groser said last week.
"We've barely started. Phony negotiating positions have been put on the table but that doesn't help a professional negotiator make a judgment as to where the landing zone is."
However, Key said: "From what I've seen at the moment, if in theory we froze time and concluded the deal as I see it, it's net positive for New Zealand.
"But it wouldn't be doing enough for dairy for us to be comfortable and we would like to do some more there.
"There are a lot of other sectors that would be very happy about it."
Key said his gut instinct was that the Senate would follow the US Congress, which by a narrow vote last week approved Obama's so-called "fast-track" authority to negotiate a conclusion to the TPP deal.
"We'll eventually get the chance to potentially get a deal before the summer recess."
Conventional wisdom among TPP negotiators is that the 12-nation deal, covering 40 per cent of world trade, must be agreed by the end of July so that it doesn't drag beyond the US summer break in August, after which the country's politics are likely to become dominated by jockeying for position ahead of the 2016 presidential election.
"It's not straightforward," said Key.
"You've still got people in the Senate who might vote against, but my gut instinct is it's very important to President Obama and they'll do their best to get there."