The Saints skipped away to a two-goal lead before half-time but were eventually pegged back to be held to a 2-2 draw by Leicester City at home on Saturday.
There were a number of Saints players who had been involved with their respective countries last week and captain Fonte, who opened the scoring for his side, felt that perhaps some of his colleagues were feeling the pinch from a busy schedule of late.
"We controlled the game in the first half," said Fonte. "But we were against a team that never gives up. We knew about that, before the game we were talking about it.
"In the second half, we weren't fresh. We dropped our intensity. We stopped pressing them. We allowed them to have the ball too much. We didn't hold the ball up front.
"And that invites pressure. It looked like a question of time when they were going to score, because it was ball after ball after ball, too much defending. When that happens, you run the risk of conceding goals and that is what happened.
"We had a lot of people away on international duty. They came back tired. You could see we were tired. Leicester don't have as many players (as us) in the national teams and it showed.
"We weren't fresh enough after 55 minutes. It's hard when you go away (on international duty) but we will talk about what we can do."
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