Mr Johnson said he will reflect on the conduct suggestions in the report
Boris Johnson's role in the Damian Green affair was "extraordinary and unwise" but did not amount to an abuse of office, a new report has found.
The independent report prepared for the London Assembly by solicitor Jonathan Goolden cleared the mayor of breaking its code of conduct.
Mr Johnson was accused of prejudging the outcome of a police investigation into Tory MP Mr Green.
The mayor said he would "reflect" on suggestions in Mr Goolden's report.
In a statement, Mr Johnson said: "He concludes that I did not fail to comply with the code of conduct of the MPA (Metropolitan Police Authority) and GLA (Greater London Authority)...I will now reflect on suggestions for the future on how to deal with extraordinary situations when they arise."
The report suggests that assembly members need to adopt a protocol outlining what is and is not appropriate conduct for members who also sit on the MPA, which oversees the police.
But Labour Assembly Labour group leader Len Duvall, who made the original complaint to the assembly's standards board sub-committee, said the warning to Mr Johnson was very clear.
"He has had a lucky escape on technicalities and been given the benefit of the doubt this time but in my view his actions were reckless, improper and made for political advantage."
The report by Mr Goolden still needs to be considered by the sub-committee responsible for conduct before the matter is officially closed.
Mr Green was arrested in November as part of an ongoing Scotland Yard probe into the leaking of sensitive Home Office information.
On 3 December the mayor told a meeting of the Metropolitan Police Authority that he believed Mr Green would be vindicated and admitted discussing the case with him.