Thompson, given his prominent position as a doubter in the lead-up to Monday's meeting at Hampden, has been portrayed as doing a U-turn over the proposals being put forward by the SPL strategy group.
However, he claims the Tangerines will NOT vote for the plan for a 10-team top flight as it stands.
He believes there needs to be greater redistribution of wealth among Scotland's leading clubs as well as movement on a host of other matters before he can back the blueprint.
Thompson also conceded, though, that when a show of hands was taken on whether to explore the option of a 14-club set-up, his arm stayed down while those representing the other "rebels" — Hearts, Kilmarnock and Inverness Caley Thistle — voted for it.
His reasoning is one of realpolitik as, with no prospect of reaching consensus on a 14, only 10 or the status quo of 12 remain as possibilities.
"If the current proposals on the table are put forward as they are they won't be voted for by us — that's the bottom line," said Thompson.
"There is a long, long way to go in all this because there are massive, fundamental things to be looked at but there was good progress made at the meeting."
He added, "I had been strong on 14 teams — it was my preferred option — but looking deeply into it, it just doesn't stack up financially.
"It is not going to happen. Eight or nine clubs are against it so there is no point.
"You have to be pragmatic with these things. Why fight for a losing cause?"
Redistribution of wealth
Thompson said, "The simple fact is that if you are in the bottom eight (when a 14-team league splits) then the figures don't work and a club like ours could lose hundreds of thousands of pounds.
"I know the fans want a 14 but there is no support for it (among the SPL clubs' hierarchy) — it's just not going to happen.
"If there is not going to be a 14 then let's look at making things the best we can. Whether that is with a 10-team league or sticking with 12, that is what we have to decide."
United will continue to lobby for more money to filter down from the top of the SPL, with a host of other non-Old Firm clubs also keen to see that happen.
Thompson said, "Distribution of funds is a big, big issue and that has not been addressed yet.
"Everyone will have to give up something, including ourselves.
"There is a lot of detail still to be sorted and redistribution of wealth is a big factor."
He added, "It was discussed on Monday that a 10-team league will only be attractive if it makes the league more competitive.
"That means a more even redistribution of the money the SPL generates."
Thompson said, "There are also a number of other big issues which need to be addressed, like parachute payments for the league below and play-offs.
"I think there is no reason we can't have a winter break and an earlier start for next season, for example. But as things stand that will only come in if it is voted as part of this package."
Thompson defended his decision not to throw his hand in with Killie, Hearts and ICT when they looked for support.
He said, "We did not have a proper vote.
"There was no show of hands for a 10-team league.
"There was a show of hands for continuing to explore a 14-team league but it was clear there was very little support for it."
He added, "I did not put my hand up for a 14-team league because I knew there was not enough backing for it.
"If there is no chance of getting it through then you are as well burying it."
Dunfermline chairman John Yorkston criticised the SPL for turning a deaf ear to the wishes of fans, insisting a move to 10 should not be seen as a foregone conclusion.
"I don't see this being steamrolled through," he said.
"I certainly don't know of any clubs in the first division who are in favour. The majority, like the fans, want a bigger Premier League."
SPL not listening to fans
He added, "The league of 10 didn't work when it was first introduced and I can see absolutely no reason why it would work now.
"I think the clubs in the lower half of the Premier League and the clubs in the first division would be more stable if it were a bigger league."
Yorkston said, "My personal choice would be a 16- or 18-team league although a league of 14 would be a lot better than 10.
"Speaking on the financial side, yes it would be nice to get more money but when you look at a 10-team Premier League you are invariably going to have five or so teams fighting against relegation.
"I would rather have a bigger league with less money because at least it would give you that little bit more stability."
He added, "Unfortunately, the SPL have not listened to the views of Scotland's football supporters.
"Surely these are people who must be taken into consideration given that we are talking about the future of the game in this country."