The Detroit Lions are cautious about the expensive prospect of adding a retractable roof to Ford Field to satisfy Major League Soccer's criteria for granting the city an expansion team.

"We're not at this point absolutely saying no to it. We're evaluating it," team President Rod Wood told Crain's last week.

There's no formal timeline that's been disclosed on a roof decision, but Wood said they will "decide soon" on whether the project is feasible and what form it might take.

Retrofitting an NFL stadium with a roof that can open and close has never been done. It's not yet known how much it might cost, but certainly won't be cheap. Wood said he doubts it would surpass Ford Field's original $500 million construction price.

"That would shock me," he said. "I'm not going to speculate on (cost) because we're just beginning the process. It's going to be an important factor."

The suggestion that the stadium could be retrofitted with a retractable roof for MLS soccer was first publicly broached by Quicken Loans Inc. Chairman Dan Gilbert in June during a session at the AXS Ticketing Symposium held in Detroit. His comments were first reported by Sports Business Daily, which stages the annual event.

"If we get that worked out, I think we have a pretty good chance" of landing an MLS franchise for Detroit, Gilbert was quoted as saying.

Nothing has been determined on who would pay for it.