Illness and a back injury prevented the pair from playing in Monday's 0-0 draw against Liverpool, with Calum Chambers and Gabriel Paulista filling in for the absent duo.
Wenger will be hoping his regular starters can soon return after their replacements were unconvincing in the first half as goalkeeper Petr Cech made two stunning saves with Liverpool playmaker Philippe Coutinho hitting the woodwork twice.
“Mertesacker is still ill and we will know more about Koscielny after he has a test,” Wenger said in his Thursday news conference.
“Koscielny will have a test today and we'll know more tomorrow,” he added.
In Monday's game, Arsenal midfielder Aaron Ramsey had an eighth-minute strike ruled out for offside and the 24-year-old called for the use of technology for marginal decisions after replays indicated the goal should have stood.
Wenger echoed the comments made by the Welshman and is confident technology will eventually be introduced to assist in that aspect of the game.
“I'm convinced it will come in. It's the next step (on offside decisions),” the 65-year-old Frenchman said.
“The sooner the better, you would have my signature on it tomorrow morning.”
The Gunners have collected just four points form their opening three Premier League games and Wenger put the club's slow start down to a lack of match fitness.
“Some players are not completely there yet. It's normal after two or three games that you're not at 100 percent,” he added.
“We've not had the ideal start. We've played three games, we want to play 60 and we've lost a game we shouldn't have.
“I said we wanted to start strong because we had two derbies and Liverpool at home.”
Arsenal have won seven in a row against Newcastle United and Wenger is confident his side can overcome what he expects to be a tough match to improve the streak to eight.
“It's important that we prepare well. It's always very tight and very committed there because the crowd is behind them,” Wenger said.
“We have always done very well,” he added. – Reuters
Original source: Defensive worry for Arsenal, Wenger