Saints manager Koeman admitted his attacking summer signings from Holland need time to adapt to England's physicality.
Southampton laboured to a goalless home draw with West Brom in league action on Saturday, prompting Koeman to admit he is still chasing further transfer window recruits.
The St Mary's outfit are understood to be pursuing both Spurs winger Andros Townsend and unsettled Atletico Madrid defender Toby Alderweireld.
Saints take on Championship club Millwall in the Capital One Cup on Tuesday night, with Koeman keen to see his side fire back to finishing form.
"I think sometimes he can be a little bit more aggressive maybe, to expect in which position the ball falls down," Koeman told the Southern Daily Echo of Pelle, Saints' Italian summer recruit from Feyenoord.
"But he needs players from the midfield and with movements around him.
"If there comes a long ball, you have to expect something.
"If you wait and you go then, sometimes you are too late."
Tadic joined Saints from FC Twente in the summer, recruited to replace Liverpool-bound Adam Lallana.
Koeman believes both Pelle and Tadic can thrive in the Premier League, but admitted they will take time to acclimatise after stints in the Dutch top-flight.
The former Holland defender could well pitch both men into League Cup action on Tuesday, to accelerate their English immersion.
"For Pelle and Tadic it's a higher level and they need to be stronger to be competitive in the Premier League," he said.
"They need time for that, because it's a big change.
"The defenders are stronger and it's more physical than in Holland.
"The qualities they have, but they need time to adapt."
Southampton are thought to have submitted an increased offer to Tottenham in their battle to prise England flyer Townsend away from White Hart Lane.
Koeman is also understood to have made enquiries to Atletico on the availability of Belgium defender Alderweireld, who has attracted attention from Liverpool, Arsenal and Napoli.
Source : PA
Source: PA