A female spectator was taken to hospital after being hit by an advertising banner that fell from the upper tier at the Halle Open in Germany.
The 62-year-old woman was sitting in the lower tier watching Alexander Zverev's match with Marcos Giron when she was struck, but did not suffer any major injuries, according to the tournament website.
Zverev handed her an ice pack, which she held to her neck as she left the stadium before going to hospital to be checked.
"There has never been anything like this in our 32-year tournament history. We deeply regret the incident," said tournament director Ralf Weber.
Weber also promised the woman a free season ticket for next year's event.
"We suspect that the drumming against the boards caused screws to come loose," event managers Dr Udo Kleine and Uwe Greipel-Dominik said in a joint statement.
"This must not happen and we apologise. We will also check all the other boards and their fixings immediately after the Zverev match."
When the match resumed, Zverev completed a 6-2 6-1 victory to move into the last 16.