Uefa says concussion substitutes are not allowed in the Women's Champions League after confusion following a head injury to Arsenal's Beth Mead in Wednesday's game against Ajax.
Mead was forced off after a clash of heads with Ajax defender Lisa Doorn.
Arsenal boss Jonas Eidevall said he was told he could make a concussion substitution before being informed that it would not be allowed.
Brain injury charity Headway has criticised Uefa over the incident.
"Arsenal team doctors followed Uefa's concussion protocols, they rightly prioritised their player's welfare and prepared a concussion substitute, it is disappointing that this substitute was not allowed on to the pitch," Luke Griggs, the interim chief executive of Headway UK said.
Uefa rules for the competition state teams can make a maximum of five substitutions within three stoppages - and there are no concussion substitutions.
There are currently no Uefa competitions, including the men's and Women's Champions League, taking part in the ongoing trial of concussion substitutions by the International Football Association Board (Ifab).
The Premier League and the Women's Super League are participating in the Ifab trial which allows two permanent substitutions to be made in the event of head injuries, even if all replacements have already been used.
Not every league or competition is taking part in the trial, which was set up to safely manage any in-game head injuries.
"It is frustrating that Uefa are not expanding the use of concussion substitutes into more competitions," Griggs said.
"Despite launching their concussion charter last year and a concussion awareness campaign, they have only allowed concussion substitutions in one competition - the 2021 Uefa European Under-21 Championship finals."
England international Mead was taken off immediately after the collision as a precaution for concussion and Eidevall said post-match that he was preparing Lina Hurtig as a replacement before his side were forced to finish the game with 10 players in stoppage time.
"Don't worry Meado's all OK!" Arsenal tweeted on Thursday. "Thanks for your concern and love, Gooners."
Griggs added: "Previously, we have seen instances of teams keeping players on the pitch after sustaining a head injury.
"Now we see a team doing the right thing, putting their player's safety first, and being penalised - forced to play the remainder of the match with 10 players.
"Through these on-pitch decisions, Uefa are undermining their own concussion awareness and player welfare campaign.
"They really missed an opportunity last night; we could have seen women's football lead from the front on this important issue."
Source: BBC
BDST: 1120 HRS, SEP 30, 2022
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