Charlie Gordon, the former Glasgow City Council leader, is considering a bid to unseat Jack McConnell as Labour leader at Holyrood, if the former First Minister does not opt to stand down first.

The Glasgow Cathcart MSP has told friends he believes there should be a contest, and that he is willing to be a "stalking horse". However, it is understood he has little expectation of winning the leadership, and that the effect would be to draw other MSPs into such a race.

Contacted yesterday, Mr Gordon would say only that he has not ruled out standing to force a contest.

The prospect adds to the pressure on Mr McConnell to stand down or call a contest at which he can defend his leadership, in the wake of being ousted from office at the election in May.

Although MSPs are away from Holyrood during July and August, speculation within Labour circles has been stepped up after a weekend briefing that made it clear Mr McConnell is minded to announce he is standing down next month.

His official position is that he has not decided, and nor has he decided when he will make his plans clear. Some close to him say he is poised to quit, and hopes to secure a new role, likely to include a seat in the House of Lords. Yet it is also claimed he is facing pressure to remain in the post and retain party stability, possibly by forcing an election in an attempt to win a renewed leadership mandate.

That speculation has made a contest all but inevitable. Mr Gordon could pressure the party's Scottish executive to call a special conference, though Wendy Alexander, the front runner to replace Mr McConnell, could be the one to put down the minimum 10 MSP nominations to spark a challenge.

On the left of the party, Elaine Smith, convener of the Campaign for Socialism grouping within the Holyrood group, told The Herald that the party membership must be given a choice, unlike the replacement in the Westminster leadership of Tony Blair by Gordon Brown last month.

The Coatbridge and Chryston representative said MSPs must not act as "gatekeepers" the way MPs did in the Commons, giving so much backing to one candidate that no-one else can win enough nominations to take their case to the wider party. She supported the left-winger John McDonnell in his unsuccessful bid to challenge Mr Brown. However, she ruled herself out as a left-wing candidate for the leadership.

One of those who could take up the left-wing mantle in a battle for the leadership could be Cathy Jamieson, who was a leading light in the Campaign for Socialism until she became a minister in 2002.

Apart from Wendy Alexander, the finance and sustainable growth spokeswoman, Andy Kerr, the health spokesman, is thought to be the second most likely candidate in a leadership contest. Margaret Curran, with the justice brief, is understood to be considering whether to stand.

A further significant figure is Iain Gray, the former enterprise minister until losing his Edinburgh seat in 2003, and then returning as East Lothian MSP in May. He could pitch to remove the party from the domination of Strathclyde, and try to win back the ground it has lost in the east and the rural parts of the country. He could also call on support from Westminster, where he has been working as a special adviser for Alistair Darling, now the Chancellor, and for Douglas Alexander when he was Scotland Secretary.

Labour rules allow a challenge to the Holyrood leadership at the annual conference, due next February, unless the party's Scottish executive responds to at least 10 MSPs nominating a challenger and calls a special conference before then. In such a contest, one-third of the voting college is decided by MSPs, MPs and MEPs combined, one-third by constituency members, and one-third by trade union affiliates.

Ms Alexander is seen as being ahead because she has put in the planning groundwork, with support expected from the Prime Minister and from trade unions.