The Hammers have brought in eight players but need to let others go as they try to balance the squad and make sure they stay within the Premier League's profit and sustainability (PSR) rules.
Kurt Zouma could leave the London Stadium while Maxwel Cornet, Nayef Aguerd and Danny Ings may be on their way out as well.
"In this time before the market closes, for everyone it's still not certain who might come and go," former Spain boss Lopetegui said Thursday.
"We have to adapt, but the competition is tough. We've tried to adapt with the new players, and we have to balance everything and try to be competitive.
"It's true that you have to keep competing in the market while working towards games."
The 57-year-old Spaniard, previously in charge of both Real Madrid and Sevilla, as well as Premier League Wolves, insisted the uncertainty was bad for his players.
"Once the market is closed I think the players are fully focused, but we have to adapt," he said. "For sure I would prefer the market to be closed before the start of the season."
Lopetegui gave full debuts to Max Kilman and Guido Rodriguez, and brought on fellow new signings Niclas Fullkrug, Crysencio Summerville and Jean-Clair Todibo, in an opening-day defeat by Aston Villa last weekend.
West Ham now travel across London to face Crystal Palace, who lost 2-1 to Brentford, in the first round of the campaign.
"Villa is in the past, and I think we have to look forward," said Lopetegui. "We have another big challenge against Crystal Palace, but we believe in ourselves and we have to show our qualities both with and without the ball in a difficult stadium."
Aaron Wan-Bissaka could make his full debut against former club Palace having moved to West Ham from Manchester United earlier this month.