Koeman has been working to lure Townsend to St Mary's before the transfer window closes on Monday, but Spurs boss Mauricio Pochettino is reluctant to sell.
"It's difficult because it's one of the players on our list, but it's very difficult and I don't expect good news about that," Koeman said.
"You can't say completely because this is football."
Southampton are hoping to claim their first Barclays Premier League victory of the season when they visit West Ham on Saturday after losing at Liverpool and drawing with West Brom.
A 2-0 Capital One Cup win over Millwall in midweek has raised confidence levels and Koeman is braced for a clash of styles at Upton Park.
"West Ham are an aggressive team and play in a physical way, different to our philosophy," Koeman said.
"It's always difficult to beat that type of team, and it will be the same on Saturday.
"Winning in the league is always important because it's the best way to gain confidence.
"You can talk and you can believe, but points bring in a good feeling.
"We lost to Liverpool and it wasn't a good game against West Brom."
Koeman kept changes to a minimum against Millwall and explained his thinking was to give his new-look team greater understanding of each other.
"We didn't make a lot of changes in the team because we are starting the season and we need to improve ourselves and get confidence," Koeman said.
"Saturday is totally different. It's the Premier League and West Ham away is different to Millwall away.
"You have to be prepared and we are prepared for Saturday."