Charlie Gordon revealed he was considering standing in the contest
The Labour MSP who solicited an illegal donation for Wendy Alexander's leadership campaign fund has expressed an interest in succeeding her.
Charlie Gordon has become the third MSP to publicly express an interest in running for leader.
He obtained a £950 donation from Jersey businessman Paul Green, which broke the rules because he is not a UK voter.
Scottish Labour deputy leader Cathy Jamieson and Margaret Curran have both said they were considering standing.
Iain Gray is also expected to stand, but bookies favourite Andy Kerr has given no indications. One MSP said he may decide not to run for family reasons.
Mr Gordon, MSP for Glasgow Cathcart, strongly supports Ms Alexander's call for an early referendum on independence.
And the former Glasgow City Council leader said the contest should not start until after the Glasgow East by-election, expected on 24 July.
Mr Gordon tells Newsnight Scotland he is interested in standing as leader
The illegal donation cost Mr Gordon his job as Scottish Labour transport spokesman, but he insisted at the time he had acted in good faith.
It was the ongoing row over donations which resulted in Ms Alexander quitting as leader.
The Scottish Parliament's standards committee recommended MSPs vote to ban her from parliament for one day after she failed to declare donations on her MSP register of interests.
Ms Alexander said she followed initial advice from Holyrood officials.