Polish media and officials have complained that the humid atmosphere in the stadium contributed to a poor second half performance by the co-hosts who had dominated Greece in the first half with an energetic pressing game.
"For sure it cost them a lot in that sauna," Polish coach Franciszek Smuda told reporters after training on Saturday.
"I could feel on the bench that it was hot, the conditions were very difficult. I think for the Russian game [on Tuesday], the roof will be open."
A spokesman for UEFA said the roof had been closed to protect Friday's game and the tournament's opening ceremony from a thunderstorm that flooded the area around the stadium two hours before kick-off.
"The roof will be open for the remaining matches taking place in Warsaw unless there are exceptional weather circumstances," UEFA spokesman Robert Faulkner told Reuters.
"This was always the plan."
