The Belgium defender joined the Premier League club on a season-long loan move from Atletico Madrid on transfer deadline day and could make his debut against Newcastle United on Saturday.
Southampton do have an option to make the switch permanent at the end of the campaign, with a fee already said to have been agreed with Atletico, who can choose to take the former Ajax man back to Spain if they decide against selling him.
Alderweireld admits he is in the dark over what is in store for him next season, but is concentrating on nailing down a place in the Southampton starting XI in the meantime.
The 25-year-old centre-back said: "There is provision that Atletico can take [me] back if [they] want to.
"For me, next year the construction is complicated. I understand. We sit down together after this season with all the parties and see what is the best solution.
"I will get the chance to show, but if I have two weeks in a row when I do not perform well, I will move to the bench.
"The football requires more from you physically than in Spain.
"The Premier League is also changing. I have four years in a row in the Champions League and have played in the World Cup - I know what excellence means."
Antwerp-born Alderweireld can also operate at right-back and is keen to secure regular football after making just 18 starts in all competitions in his first season at Atletico.
"I hope to accrue games weekly in a top competition like the Premier League," he added.
"Not that I have bad memories of my first year at Atletico, I became more mature and could play in the Champions League, but in the centre of defence the team was already there from the year before, so it was difficult for me to get into it.
"Atletico understood that I wanted a year away."
