Steve McClaren described Daryl Janmaat's red card as "harsh" and believes the full-back's dismissal cost Newcastle United in Saturday's 2-0 Premier League defeat at Swansea City.
Goals from Bafetimbi Gomis and Andre Ayew were enough for Swansea to pick up the win at the Liberty Stadium.
However, Newcastle's task was made harder when Janmaat was dismissed shortly before the break by referee Mike Jones for two clumsy challenges on the impressive Jefferson Montero.
"I thought it [the sending off] was harsh, he's a long way from goal," head coach McClaren said. "Okay, Daryl had made his presence known, he needed to do it, but it was a little tug.
"The referee could have been lenient but we can't control it, he gave it. I'll complain but it will be a limp one. From then on it's very difficult.
"The first yellow he made his intentions clear the referee. If we learnt anything it was emotional control and that's cost us. The only lesson we can learn is to keep 11 players on the field.
"We learnt so much last week, but learnt nothing apart from we need to keep 11 players on the field. You can't win in the Premier League with 10 players, it's difficult against a good Swansea team."
McClaren was also dealt a blow when Moussa Sissoko had to be replaced at half-time.
"He's got a groin strain," McClaren added. "Ten men then losing Moussa, we lose a big threat. We don't know the seriousness of the injury yet."
