The Pensions Secretary David Blunkett should be "allowed to get on with his job", the British Prime Minister has said.
Mr Blair is seeking advice over claims Mr Blunkett's involvement in a DNA testing firm broke ministerial rules and constitutes a conflict of interest.
And speaking in Downing Street, Mr Blair warned people not to "rush to a conclusion".
Downing Street has repeatedly insisted Mr Blunkett retains the PM's confidence despite the latest controversy.
Conservatives are demanding a full investigation into whether he broke the ministerial code of conduct by accepting a directorship without consulting an advisory committee.
Mr Blunkett also faces questions over his decision to buy shares in the firm for his sons.
Mr Blair's official spokesman said it was "quite reasonable" to seek advice on issues of interpretation, saying the PM "wants things to be clear".
The issue was later raised with Mr Blair himself at a press conference in Downing Street.
"I do give him my confidence. In respect of the allegations about the shareholding I know David is looking into that. He has been dealing with other things today," he said.
"But I think that he should be allowed to get on with his job, which is very important, reforming and reshaping our welfare system. I don't think people should rush to a conclusion until we actually know what has gone on."