Liverpool City Council has agreed to spend £4m on improvements to Everton Football Club’s training ground.
The Finch Farm training complex, owned by the council, is rented to the Premier League club.
The improvements include a recuperation suite for injured players, a new block for groundsmen and a ‘show pitch’ or mini-stadium.
The council’s cabinet said it is a good investment, but critics have questioned the use of taxpayers’ money.
Liberal Democrat opposition leader Richard Kemp said: “The further investment into Finch Farm is an investment shrouded in mystery.
“Why cannot the terms and conditions for this be made public?
“EFC now have a backer and more money – why cannot they finance it themselves?
“The Lib Dems have nothing against this development in principle, but these are the basic questions which are not mentioned in the report.”
Liverpool mayor Joe Anderson insisted the rent will increase by more than 3% because of the improvements.
He said: “It’s a fantastic deal for us and the city of Liverpool.
“It is like when you buy a house and you rent it out. If you want to put an extra room on it, you’ll make sure it brings you extra revenue.”
The council has defended the investment despite Finch Farm being in Knowsley, outside the Liverpool city boundary.
A council spokesman said: “This is a commercial arrangement which is an exceptionally good deal for council tax payers as we can reinvest the profits in delivering front-line services.
“In the first two years, we have already made £400,000 that we would not otherwise have had.
“The new investment will be paid back through additional rental income over the remaining term of the lease.”
Analysis – BBC Political Reporter Claire Hamilton
This is one of the schemes which mayor Joe Anderson calls “invest to earn”. It’s one of his flagship policies and something he’s very proud of.
The idea is that the council buys an asset – sometimes borrowing money at a very low interest rate – and then rents it to an organisation to make a profit in the long term.
Now, as we know, the council’s funding from central government has reduced over the past six years so they’ve had to be creative when it comes to generating income.
The council bought Finch Farm in 2013 for about £13m and rented it to Everton on a long lease.
They’re getting about £200,000 a year profit and the lease has nearly 37 years left to run.