Bayer Leverkusen coach Kasper Hjulmand questioned whether Champions League opponent Arsenal's set-piece tactics are legal ahead of Wednesday's last-16 first-leg tie in Germany.
Speaking at a press conference on Tuesday, Hjulmand asked whether blocking opponents should be permitted, particularly with the influence of set pieces in the game growing.
"It's a big challenge but I have to say, I'm a bit confused by these offensive blocks. I don't know if it's allowed under the rules when the ball is very far away," Hjulmand told reporters.
Mikel Arteta's side sit on top of the Premier League thanks in large part to their success from set-pieces.
They equalled the Premier League single-season record for goals from corners with two in their 2-1 win over Chelsea to reach 16 for the campaign.
In the Champions League, Arsenal won eight from eight to finish atop the 36-team table.
"We also do it, so it's not just something others do. But it's getting more and more common in football," Hjulmand said of the practice.
"There are very many blocks and they (Arsenal) create a lot of chances as a result of it.
"They do it very well and spend a lot of time on these situations. They're one of the best teams in these situations and they work with it a lot."
The Dane said he thought blocks were only permitted close to the ball.
"As I understand football, when you do body checks the ball has to be inside a playing situation.
"So I'm just wondering – is it inside the rules to actually block without the ball being close to you. Creating space, pushing players, pushing the goalkeeper?"
Hjulmand was the latest to join the chorus critical of Arsenal's tactics.
Earlier in March, Brighton coach Fabian Huerzeler hit out at Arsenal's time wasting, saying "only one team wanted to play football" in their 1-0 defeat to the league leaders.
Former Chelsea striker Chris Sutton questioned whether Arsenal could be the "ugliest" Premier League winners in history after their victory over Chelsea.
But the Premier League leaders have embraced the criticism, with fans chanting "set-piece again, ole, ole".
Before the Brighton clash, Arteta told reporters he is "upset that we don't score more" from dead-ball situations.