Andy Robinson said "there will be consequences" following Scotland's 21-15 Test loss to Tonga in Aberdeen.
Scotland's first defeat to the South Pacific side was their third loss in the autumn Test series and places a question mark over Robinson's future.
"That was a totally unacceptable performance we've witnessed today," Robinson said.
"I'm very angry - there will be consequences because of this performance. It reflects on me."
Asked about his own future, Robinson added: "We'll look at everything - I've got to look at myself, as has everybody involved.
"I've got a contract and my focus at the moment is talking to the players."
Two Greig Laidlaw penalties to one by Fangatapu Apikotoa gave the Scots a narrow and deserved half-time lead, as they looked to recover from autumn international defeats to South Africa and New Zealand in their two previous outings.
But, after the break, Tukulua Lokotui squeezed over the line and Apikotoa dinked over the conversion.
Three Laidlaw penalties were not enough for the Scots as Fetu'u Vainikolo added a second try for the Tongans.
And Robinson admitted his side had been second best against the South Pacific islanders. He said: "We've underperformed and if we underperform we're going to get beat and that's what happened.
"We got opportunities close to the line with the maul but we weren't able to get the ball down on the line.
"Tonga squeezed us with the amount of penalties they gave away, that made it a disjointed game."
Robinson also admitted that Scotland had allowed Tonga to control the physical aspects of the match.
"They dominated us at the tackle contest and if you get dominated at the tackle contest you end up being in a fight for the game," he said.
"It became a fight and Tonga scored a try and they were able to hold on.
"There are a couple of key areas for us. Our tackle technique and our tackle contest work is key: the core skills are vital.
"We go now to take on England at Twickenham [in the Six Nations] where we have not won for 30 years."
Tonga coach Mana Otai was delighted with his side's performance and said the result ranks as one of the best in his country's history.
"The boys wrote a bit of history for themselves," he said. "Last year we beat the French; back in 1973 Tonga beat the Wallabies - occasions we don't forget easily."