Pochettino also had to take off several players.
"Adam Lallana had a knock after coming together with another player on the neck and that is why he couldn't continue," said the Argentinian.
"Danny Fox had a knock on (his) quadriceps, which led to him being substituted as well.
"We do not know how serious it is. In the next couple of days we will do the necessary analysis."
The injuries capped a bad day at the office for Southampton, who were outfought at St Mary's.
"We have to accept that because we made some mistakes," Pochettino added. "We've tried very hard. We've put in a great effort to try and get a different kind of result.
"But because of some mistakes we have made and their goalkeeper's intervention a couple of times we didn't get a positive result."