Birmingham midfielder Charlee Adams has signed a new one-year contract with the club.
Southampton are confident Jay Rodriguez will commit to a new long-term deal but the player will consider his options.
The former New York Red Bulls and Wigan centre-back scored the Terriers' fourth goal, turning home in a crowded area.
Talking about the former Sweden international, Robins told the official website: "This was a good opportunity to look at Markus and he's done nothing wrong.
"He's a not a youngster - he's 29 - and we have to make a decision on whether he can perform in the Championship on a consistent basis."
Holgersson has spent the majority of his career in his homeland, playing for Angelholm and then Helsingborg.