The councillor in charge of Birmingham's bin collections said there was "no overnight fix" after it was revealed last week that rubbish in the city was still going uncollected.
John O'Shea admitted that up to 900 collections were missed every day and told a council meeting on Tuesday that he was "under no illusions the service is not delivering".
"The problems are quite serious and need to be resolved," he said, explaining that there were lingering problems regarding routes and structures after workers changed from a five-day week to four.
However he said he was "confident they will be resolved and we will make the service better".
Refuse collections in Birmingham have been disrupted twice since a strike in 2017 about the changes to working patterns.