The winger, who has been on international duty with Senegal, might not arrive in England in time to make make the squad for the Premier League fixture.
"He had to travel to Ghana to get his stamp (visa) to get to England so it will be a late decision if he is available to play," Koeman told reporters.
"He will travel [to England] tomorrow. If he is part of the team he will start on the bench. Sadio brings a different quality to the team, he is a player who is fast and has a good record for goals.
"We don't have a lot of forward players so his qualities bring a little bit more, he is difficult for defenders to mark."
Koeman could hand a debut to another deadline-day capture, defender Toby Alderweireld, against Newcastle.