|Date of birth||20 August 1965|
|Place of birth||Dakar, Senegal|
|Height||1.78 m (5 ft 10 in)|
* Senior club appearances and goals counted for the domestic league only.
In November 1996, Dia famously convinced then-manager of Southampton, Graeme Souness, that he was the cousin of FIFA World Player of the Year and Ballon d'Or winner George Weah, which led to him signing a one-month contract with Southampton just days later. Dia played only one match in his short spell at the club before being released 14 days into his contract.
After a playing career at the lower levels in France and Germany, and having already had failed trials at Port Vale, Gillingham, and Bournemouth, Dia joined non-league club Blyth Spartans, where he made only one substitute appearance – on 9 November 1996 in a Northern Premier League game against Boston United.
Days later, Dia was signed by Southampton manager Graeme Souness, after Souness received a phone call purporting to be from Liberian international and former FIFA World Player of the Year, George Weah. "Weah" told Souness that Dia was his cousin, had played for Paris Saint-Germain, and had played 13 times for his country. None of this was actually true, and the phone call to Souness was made by a fellow university student of Dia's, suggesting that he should give Dia a chance with Southampton. Souness was convinced, and without any due diligence, Dia was signed on a one-month contract.
Dia played just one game for Southampton, wearing the number 33 shirt, against Leeds United on 23 November 1996; he had originally been scheduled to play in a reserve team friendly against Arsenal, but the match was cancelled due to a waterlogged pitch. In the match against Leeds, he came on as a substitute for Matthew Le Tissier after 32 minutes, but was later substituted himself (for Ken Monkou) in the 85th minute; Leeds won the match 2–0. Le Tissier said: "He ran around the pitch like Bambi on ice; it was very embarrassing to watch."
Dia was released by Southampton two weeks into his contract. He briefly played for non-league Gateshead, before leaving in February 1997. Dia only played eight games for the North East outfit, including scoring on his debut in a 5–0 win over Bath City.
Dia has achieved a notorious status amongst English football fans for his lack of ability, and is regularly featured in lists of bad players or bad transfers. Dia was named at Number 1 in a list of "The 50 worst footballers" in The Times newspaper and in a list of the "Top 10 rubbish footballers" published in The Sun newspaper, and at Number 4 in a list for the Top 50 worst strikers according to the Daily Mail.
- Alessandro Zarrelli: Italian footballer who gained similar notoriety
- Hills, David (6 August 2000). "The 10 worst foreign signings of all time". The Observer. Retrieved 18 December 2012.
- "Never again...". BBC Sport. 1 April 2003. Retrieved 18 December 2012.
- Holley, Duncan; Chalk, Gary (2003). In That Number – A post-war chronicle of Southampton FC. Hagiology Publishing. pp. 248 & 504. ISBN 0-9534474-3-X.
- Gibbs, Thom (7 February 2011). "Five terrible debuts to make Fernando Torres feel better". Daily Telegraph. Retrieved 18 December 2012.
- "The one-off who played for Southampton". Guardian. Retrieved 3 December 2013.
- "The Journal of Failure". The Legend of Ali Dia. Retrieved 3 December 2013.
- "Gateshead F.C. Season 1996/97". Unofficial Gateshead Football Club Statistics Database. Retrieved 23 July 2011.
- Harris, Nick (17 May 2006). "Meet the BBC's guest editor (and other accidental heroes)". The Independent. Retrieved 18 December 2012.
- "Premiership's Top 10 Foreign Flops". Who Ate All the Pies?. 25 May 2008. Retrieved 18 December 2012.
- Murphy, Alex (4 July 2007). "The 50 worst footballers". The Times (London). Retrieved 20 July 2007. (subscription required (. ))
- Glicksman, Gavin (23 February 2009). "Top 10 rubbish footballers". The Sun. Retrieved 18 December 2012.
- Bellwood, Tom (9 October 2009). "The worst strikers to have played in the Premier League". Daily Mail. Retrieved 18 December 2012.