The lessons from baseball
At present, there are no U.S. baseball teams traded as free-standing entities, but there are three clubs under ownership of publicly-traded firm. Each share a common thread: once they were bought up, the trophies dried up.
The Seattle Mariners set a record of 116 wins a season in 2001. They were then bought by Nintendo in 2004 and have struggled ever since. They ranked near the bottom in almost every major category in the American League for 2013 including batting average, on-base percentage and total strikeouts.
The Toronto Blue Jays, World Series winners in both 1992 and 1993, were acquired by Rogers Communications in 2000 and have not won anything since.
And the Atlanta Braves last won a World Series in 1995 when they were privately held by CNN founder Ted Turner. Since being taken over first by Time Warner and then by Liberty Media, the team has made it to the Series but never managed to win it.
The conclusion is clear: business and sports do not coalesce. Just as the sale of Babe Ruth (sometimes called "The Bambino") from the Boston Red Sox to the New York Yankees created a "curse," whereby the former team went 86 years without winning a World Series, perhaps there is a similar correlation between a public traded company and trophies.
"Of course it's something to worry about; massively," said Michael Jarman, chief strategist at H2O Markets and an avid (Manchester) United fan. "It's not just with clubs that are public-traded; it's anyone who takes a hold of a football team and tries to run it like a business.
"Now, when the world's best player is up for sale, United won't be able to get them. We can afford him, in theory, but we've now got a duty of care to try to get a return for our shareholder without running the business into bankruptcy."
Player purchasing power
United listed 10 percent of the company on the New York Stock Exchange in the summer of 2012. At the end of the 2012-2013 season, however, they clinched the Premier League title, a record twentieth English league championship. Yet Jarman argues that was down to the acumen of Sir Alex Ferguson, who retired last year after 26 years in charge.
(Read more: Hedge funds bet against Manchester United)
Jarman contends that Ferguson's signing of Robin van Persie, £22.5 million, was a good deal as it came at the end of the striker's contract with Arsenal. He argues that Ferguson this season would have been constrained by the team being listed on the stock market and by the rebuilding of Manchester City and Chelsea, who have all spent big.
"He left on a high, he timed that to perfection,"Jarman said. "Although the performances would not have been as bad as this season (if Ferguson had stayed), he would have been up against it and there was nothing he could have done to still compete with Chelsea and Man City."
All the major clubs - owned by rich businessmen and unhindered by share price concerns - are now spending more and more than ever before. Before the start of today's transfer business, Premier League clubs had spent around £95 million on new players during January's window, £10 million more than last year.
The combined transfer spend of English top-flight clubs this season has already passed the £700 million mark for the first time, ahead of any deals struck today, according to Deloitte.
Jarman points to Arsenal, which while not public-traded, has been dictated by a model that puts business and profit ahead of on-the-pitch success. The team is more financially secure than most other clubs, but has not lifted a major trophy in nearly a decade. Fan anger finally forced their owners to fork out £42 million for Mesut Özil last summer, and they are now title contenders.
Though heavy spending clearly doesn't guarantee wins in baseball by itself, the World Series winners over the last decade are without exception free-spending and privately held: the Boston Red Sox, San Francisco Giants, St.Louis Cardinals, Philadelphia Phillies, Chicago White Sox and the famously profligate New York Yankees.
(Read more: The big money behind the Cardinals, Red Sox)
While United has bought Mata and may secure a potential new £300,000-a-week contract for striker Wayne Rooney, this has had negative ramifications.