The move was made after Southampton recalled him from MK Dons.
Seager links up with the Glovers for the remainder of the season, as he looks to aid their League Two campaign.
The 21-year-old had been on loan with MK Dons, making eight starts and six substitute appearances in League One, but the club took the decision to recall him in order for him to gain further playing time with Yeovil.
Meanwhile, Saints defender Wesley Hoedt has urged fans to stand with them.
He said, “We have to stick together, not only the team but the fans. It's been difficult for them because we haven't taken many points but they have to stick behind us and together we can do it."