Scotland coach Townsend unhappy with officials after captain Ritchie sidelined
Ritchie was struck in the head following a tackle from Tongan winger Afusipa Taumoepeau late in the first half of the Pool B clash in Nice.
Taumoepeau was given a yellow card by referee Karl Dickson, which was not upgraded to red on bunker review.
"It will be a 12-day turnaround I would imagine as he has had previous head injuries," Townsend told reporters. "That is obviously a big blow for him and for us.
"It was very disappointing for our captain and one of our key players to be removed from the game. Against South Africa, Jack Dempsey was also hit in the head and nothing was done that day."
World Rugby has introduced a bunker system where officials have eight minutes to decide on review if a yellow card should be upgraded to a red, or vice-versa.
"I just don’t understand what the bunker television match official and three (match) officials are looking at to say if it is a red card or not," Townsend said.
"It seems they are looking for ways not to give red cards, rather than referee what is an illegal tackle."
Townsend was pleased with the bonus-point win which keeps his team’s quarter-final hopes alive and, assuming they get five points from their next match against Romania, sets up a showdown with Ireland in Paris on October 7th for a knockout place.
"Tonga tested us in contact areas, at the rucks they are a very good side. They are very quick at winning the ball and they are hard to move. The scrum was a competitive area," he said.
"Their ball carrying was really good, the forwards have skill and their backline players are aggressive."
Townsend also confirmed hooker Stuart McInally is out of the World Cup with a neck injury, bringing to an end his international career having announced he would retire after the tournament.
"He had pain in his neck which did not recover for two days. We did a scan and it showed (the damage)," Townsend said.
Johnny Matthews will join the Scotland squad in France as a replacement.