London 2012: Olympic football kicks off at Hampden
Glasgow kicks off its Olympic duties later as the US women's football team takes on France at Hampden.
The match, along with the Colombia v Korea DPR women's tie which follows it, is taking place two days before the Olympics officially begin.
More than 40,000 fans are expected to watch the opening games at the national stadium but about 34,000 were given away rather than paid for.
A total of eight games are due to be played there over the next 10 days.
BBC Scotland's Olympics correspondent Kheredine Idessane said officials did not know how many people would turn up for Wednesday's games at the 52,000-seater stadium.
He said: "They have issued 41,000 tickets but they have actually only sold 6,500. More than 34,000 have been given away to youth groups, charities and sports clubs.
"It all depends on how many people turn up who have been offered these free tickets."
BBC Olympics coverage online
Last week London 2012 withdrew half a million Olympic football tickets after initial poor sales.
The three men's games being played at Hampden involve Honduras, Morocco, Japan and World Cup holders Spain.
The five women's games involve USA, France, Colombia and Korea DPR.
Strathclyde Police has warned those travelling to the games at Hampden to arrive early as tightened security measures in and around the stadium may lead to delays at the turnstiles.
Match commander Ch Supt Andy Bates said: "Strathclyde Police's priority is to make sure that events are safe and secure for all spectators, athletes and the people of Glasgow.
"We would really appreciate the co-operation of the public in helping to make the security operation run as smooth as possible."
The official opening ceremony for the London 2012 Olympic Games take place on Friday.
The football games to be played at Hampden include:
- the women's preliminaries on 25 July - USA v France will kick off at 17:00, followed by Colombia v Korea DPR at 19:45
- on Thursday 26 July there will be two men's preliminaries - Honduras v Morocco will kick off at 12:00, followed by Spain v Japan at 14:45
- two more women's preliminaries will be held on Saturday 28 July - USA v Colombia will kick off at 17:00, followed by France v Korea at 19:45
- the final men's preliminary to be held at Hampden will be on Wednesday 1 August, where Egypt v Belarus will kick off at 14:30
- the last Olympic football match to be played at Hampden - the women's quarter final - will take place on Friday 3 August at 12:00. The winner of Group F will play the runner-up of Group G.