Manchester United are missing out on more than £26m a season in potential revenue for Old Trafford naming rights, according to finance advisors Duff & Phelps.
A study has found United are not capitalising on the potential to bring in extra revenue from selling the naming rights to Old Trafford, which could amount to £7m a year more than Manchester City, who currently earn £19m a year from Etihad's sponsorship of their ground.
It also claims the value of the naming rights market in the Premier League has risen by 80 per cent from £74.6m in 2013 to £135.6m in 2017, with the English top flight's 'big six' accounting for more than three-quarters of that sum.
Trevor Birch, head of UK sports at Duff & Phelps and a former chief executive at Chelsea and Everton, acknowledged that these valuations were "not an exact science" and told Press Association they were "potential, theoretic valuations that might not be achievable on the market".
"It's an emotive topic, particularly in this country, but it's an area that is definitely under-utilised as a revenue stream," Birch said.
Newspaper reports have repeatedly suggested United have no intention of selling the naming rights to their 75,000-seater stadium.
The study ranks Chelsea's Stamford Bridge as potentially the third most valuable naming rights deal in the Premier League, with the defending champions able to command £18m a year.
Tottenham's new White Hart Lane ground will be worth £15.5m annually - marginally more than the £15.3m north London rivals Arsenal generate from their deal with Emirates.
Liverpool's recently-expanded Anfield is in sixth place at £11.1m, but the study suggests this is a reflection of the fact the naming rights to famous old grounds are not particularly attractive to sponsors as the original names are heavily associated with the stadiums - a point that could also be made about Old Trafford.
The evidence from North America, where naming-rights deals are common, suggests sponsors are also reluctant to take on a ground that has previously been sponsored by somebody else, as the name tends to linger. This explains why new stadia, whose names have not yet stuck, are worth a premium.
Eight Premier League clubs, including Bournemouth, Brighton, Stoke City, Huddersfield, Leicester and Swansea, currently have stadium naming rights deals.