Vitesse captain Guram Kashia has admitted that his side were "unlucky" to be drawn against Southampton in the Europa League third qualifying round.
The Dutch side will travel to St Mary's for the first leg of their tie tomorrow evening as the Saints gear up for a maiden European campaign since 2003-04.
Koeman's men impressed in the Premier League last season, but despite acknowledging them as the strongest team in the draw, Kashia backed his side to upset the odds.
"I know they are one of the good teams in the Premier League and the Premier League is the best league in the world, in my opinion," he told reporters.
"They have a Dutch coach and many players from the Dutch division. They have many strong players and are very good. Of course, it's a tough game and we were a little bit unlucky with the draw with the strongest team.
"We cannot complain right now. We have what we have got and we have the power in the team to surprise a team like this."
Southampton's last foray into Europe saw them crash out of the UEFA Cup in the first round at the hands of Steaua Bucuresti.
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