The Hoops boss was critical of his players for their lack of intensity, but was quick to congratulate the opposition on their performance.
"In the first half we had three very big chances and they had nothing. The second half was more even and we were too passive," he told BBC Sport.
"I wanted more intensity in the final 20 minutes but Inverness played well, so congratulations to them."
The defeat leaves Celtic in fifth place in the table after three matches, but they have a match in hand on all four of the teams above them.