But former Everton goalkeeper Southall, Wales' most capped player with 92 appearances, said: "I think it opens a can of worms.
"The whole point of going to the Olympics is that special moment when your flag goes up. What flag are they going to put up if they win it? The Union Jack? It's not my flag. My flag's a Dragon.
"As a Welshman I'd rather play for Wales if I was in the Olympics. I would want to go and represent my country.
"I don't see the point having a Great British team. You will just lose the identity of all the teams."