The loan will be the first of Seager’s career so far, as the 19 year-old looks to gain valuable Football League experience.
After impressing for Saints’ development side during the 2014/15 campaign, Seager made his professional debut as a substitute in last season’s FA Cup clash with Crystal Palace, before making his Premier League debut against Swansea City.
The striker has scored seven goals for Martin Hunter’s Under-21s this season, while also being named on the bench for Ronald Koeman’s first team on a number of occasions.
Crewe, who currently sit 23rd in League 1, have gained a reputation for playing entertaining football over the last few seasons.
Seager could make his debut for Steve Davis’s side when the Railwaymen take on Millwall at the Den on Saturday.