Premier League football clubs are missing out on millions of pounds in stadium naming rights, a report says.
Financial advisors Duff & Phelps say "clubs are not utilising naming rights revenue to their full potential".
Only 30% of top flight teams have a stadium sponsor, compared with more than 80% in American football's NFL.
The six 2018-19 season teams with a stadium sponsor were Bournemouth, Arsenal, Brighton, Huddersfield Town, Leicester City and Manchester City.
Of these, the report says that only Bournemouth and Huddersfield have stadium deals that are independent of their shirt sponsor and owner.
Newcastle United have also previously had a naming rights deal, which lasted just one year.
The potential value of Premier League stadium sponsorship deals increased by 5% from £135.5m in 2018 to £142.0m in 2019, according to the report.
It estimates the most valuable stadium asset to be Manchester United's Old Trafford ground, worth a potential £26.75m a season to the club.
The current so-called Big Six clubs dominate in terms of value, which is based on things like shirt sponsor and technical partner values, social media followers, TV rights, transfer spending and team performance.
Top ten Premier League stadium rights values
- Manchester United - £26.75m
- Manchester City - £21.90m
- Tottenham Hotspur - £17.50m
- Liverpool - £16.90m
- Chelsea - £16.75m
- Arsenal - £16.65m
- West Ham - £5.55m
- Newcastle United - £3.90m
- Everton - £3.30m
- Leicester City - £3.20m
Source: Duff & Phelps
The report also suggests that Liverpool have added significant value to the value of Anfield ground in the past year, thanks to their Champions League and Premier League exploits.
"Multimillion-pound Premier League shirt sponsorships have been signed, multimillion-pound sleeve sponsorships are being signed, and it is only a matter of time until multimillion-pound stadium sponsorship follows," says Michael Weaver, managing director at Duff & Phelps.
"Brands just have to be courageous enough to take the first step which will bring the market alive."
But long-term Liverpool fan Joe Blott said any benefits that might come from a rights deal must also be used to benefit fans and not just boost club coffers.
"The Premier League is already awash with sponsorship," he says.
"I understand that clubs might have to look at other sponsor options, but if they did go down that route they should look at the whole club family - not just using money to buy players, but also to drive down ticket prices. "
He added: "I, and many others fans I think, would always continue to refer to grounds as Anfield, Goodison, Old Trafford, even if deals were done."
In the US, 26 of the 32 teams in the NFL are capitalising on the branding potential of their sporting arenas.
The finance industry is the largest industry sponsor, sponsoring a quarter of named stadiums.
The NFL's most valuable contract is between the Dallas Cowboys and AT&T, which is worth £14.3m per season. The average stadium naming rights agreement is £6m per season.
Meanwhile, European football's most mature naming rights market is in Germany, where 80% of stadiums are sponsored.
By way of contrast, only 17%, or three teams, from Italy's top flight have a stadium naming sponsor.