Scotland coach Frank Hadden felt Scott Murray's kick at Wales' Ian Gough, which led to the Scotland lock being red-carded, was accidental.
Hadden admitted he had not seen a good angle of the incident, but added: "It looked pretty accidental.
"Scott was trying to get out of the tackle situation as quickly as he could and flicked out his foot.
"He wasn't looking in Ian Gough's direction at the time, so I think it's going to be a difficult one to judge."
Hadden stressed that Murray was not a dirty player, adding: "He was extremely disappointed and remorseful."
Scotland captain Jason White said: "Scott said it wasn't intentional and that it was harsh that he was sent off.
"But the referee said he saw Scott's foot hit him in the face and he had no alternative but to send him off.
"It is obviously hard when you are a man down so early, especially with the game Wales like to play where they keep the ball alive and play with width."
Despite the defeat, Hadden had nothing but praise for his players.
"That was an extremely gutsy effort from our players. There was no shortage of commitment," he said.
"Despite the circumstances with the early sending-off we created enough chances to make it extremely close at the finish but Wales were a bit more clinical when the chances came along.
"There was never a doubt that our team wouldn't battle on. Even at half-time all we talked about was how we could win the game but it was a big blow when Wales scored again 10 minutes into the second half.
"We have to give credit to Wales for their clinical finishing."