After losing captain Adam Lallana, Luke Shaw, Dejan Lovren, Calum Chambers and Rickie Lambert in the close-season, Southampton's resolve in the transfer market is expected to be tested due to their success in the league.
Southampton - fifth in the Premier League standings heading into Sunday's clash with Liverpool - could lose Nathaniel Clyne, Morgan Schneiderlin and Jay Rodriguez at the end of the 2014-15 campaign.
But Koeman has issued some advice to his players as Lallana, Lovren and Lambert prepare to return to St Mary's, warning them that the grass is not always greener on the other side.
"A reason to move is not always for the player to do about football," Koeman said. "Maybe it's about money.
"We can't pay salaries like the big teams in the Premier League pay. It's always less here.
"If you stay, you stay for different reasons. You stay for the fact you are more sure that you play every weekend and it's not too early - it's about the age of the player and about the experience of the player.
"But I think it's normal that you will lose players if you don't play every season in the Champions League because it's the intention for every player to be part of that."
