Arsenal manager Arsene Wenger, whose team have slipped to fourth in the table behind Tottenham Hotspur, bemoaned his side's lack of conviction but Koeman had no doubt about which player had made the difference between the teams.
"It was a massive performance from Fraser today. He was the key to get one point because normally we are not a defending team that allows opponents to create those kind of opportunities," the Dutchman told the club's website (www.saintsfc.co.uk).
"He's back and it's a fourth clean sheet in a row.
"That's unbelievable after nine months out. You have other good goalkeepers, but for sure he will be back in the national team."
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Forster lost his place in Roy Hodgson's England squad to Stoke's Jack Butland but his recent performances suggest he will be pushing for a place at Euro 2016.
The keeper was reluctant to take all the credit for his team's hard-earned point at Arsenal, however.
"It was a fantastic team performance. Coming away to the Emirates you know you have to work really hard and we put in a really big shift," he said.
"I'm just happy to contribute. I'm delighted to be back playing football and given the opportunity to do what I love."
The draw saw Southampton move above Liverpool into seventh place in the league.
(Reporting by Simon Jennings in Bengaluru; Editing by Peter Rutherford)
