If it goes ahead, they will join AC Milan, Atletico Madrid, Barcelona, Inter Milan, Juventus and Real Madrid in a new midweek competition.
The league is bound to lead to clashes with the Premier League and other local leagues and has led to widespread criticism from Boris Johnson, Uefa and the Premier League.
Many have accused the clubs of “greed” but investors were clearly keen on the idea.
Manchester United shares were up $1.56 at $17.72, adding around $289 million to the paper value of the club.
Juventus was up 14c at 91c, adding e216 million to its stock market value.
David Bick, football analyst and chairman of Square1 Consulting, said the share moves were based on a naive belief that the new league would ever get off the ground.
“I just can’t see it happening,” he said. “I have never seen a project so universally condemned, so quickly.”
He added that attempts to form breakaway super leagues in the past had always failed due to opposition from national leagues and lack of interest from fans.
“Supporters’ main interest is to see domestic football. I mean, how many times a year do you want to see Man United play Atletico Madrid?”
He suspected the idea, which claims to have a $6 billion package behind it organised by JPMorgan, had been ill-thought out by Americans with little understanding of the European mindset.
“They seem to be seeing this through American eyes. They do not seem to see we do not have the appetite for closed shop leagues over here.”
European football thrives on the excitement of promotion and relegation, not the “invitation only” NFL-style model, he said.