The Uruguyuan was absent as Saints drew 2-2 at home to the Cottagers, with Jose Fonte heading home late on to secure his second goal of the day as well as a vital point for his side.
"Gaston picked up a dead leg in training on Thursday," Adkins told Sky Sports.
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Adkins was happy with his sides performance in the first half but suggests they didn't maintain the intensity into the second period.
The point takes them out of the bottom three but the Saints still only have the one win to their name.
He added: "From 1-0 up, it's two points dropped.
"We did well first half. We pressed the ball well, got on the front foot, played a good high line and we scored a good goal from a set play and forged some good opportunities. Second-half we didn't maintain that high line of pressing.
"Fulham are a good side, it isn't a case of willingly beating Fulham. But we need to be picking up maximum points at home."