The midfielder has been out with a knock since the 3-0 win over West Brom in mid-January, but has trained all week and is ready for the visit to the Liberty Stadium.
Koeman also has Matt Targett available again after he missed last weekend’s 1-0 win over West Ham.
"Steven Davis is back,” Koeman told youtube.com/southamptonfc
. “He's back in the team, he did a good week of sessions in training and no other updates.
“Still Jay Rodriguez is out, Florin [Gardos] is out. Victor [Wanyama] we know is suspended and the rest of the players are available.
"It's important for the last part of the season to have everybody available and we know Steven is an important player for the team, he is an experienced player and I am happy that he is back.”
Koeman also explained that Rodriguez is edging nearer to a return to training.
"He's closer, but maybe next week or the week after that he will be part of the team session,” said the Saints boss. “That's the next step.
“It takes a long time, he needs to be patient. It's not easy always to be patient, but we know his situation and we have the total confidence that he will come back like before.”