Fernando Santos lamented conceding a late counter-attacking goal as Portugal slipped to a 1-0 defeat against Russia on Saturday.
Russia racked up a fifth straight win in the friendly encounter in Krasnodar thanks to captain Roman Shirokov's 89th-minute strike.
The hosts had also hit the crossbar through Artyom Dzyuba, while Shirokov had missed two great chances before his goal.
Santos was disappointed to concede so late in the game and admitted Portugal did not use the ball well enough in the second half.
"We ended up penalising ourselves," he said. "Conceding a goal after 89 minutes on the counter-attack is not acceptable.
"In the second half we were not so successful, especially in offensive terms. We played fairly well but lacked ability to get ahead."
Santos was happy with the way Portugal recovered from a slow start, adding: "In the first 10 minutes we found no way to play.
"But then we were able to find balance and create good situations too."