Manchester City were extremely busy on Tuesday, signing defender Aymeric Laporte from Athletic Bilbao in a reported £57million deal before bringing in English midfielder Jack Harrison from sister club New York City.
Speaking live on Football Focus, Mowbray said: "There's no sign of him and I don't think we'll be seeing him at all".
The AWOL Algerian, who also missed the defeat at Everton, has not been seen by the club since his proposed move to Manchester City collapsed on Wednesday.
"Manchester City didn't get the player they wanted".
His goals and assists - mostly for pal Jamie Vardy - turned more than a few heads, with Mahrez constantly tipped with a move away ever since, namely to Arsenal.
Mahrez has been a key player for Leicester as they have lost just one of their last seven games in all competitions. Yet one month into his reign, it is hard not to spot a unusual alchemy being worked in south Wales. I have a degree of sympathy - and only a degree - because he's under contract and should be doing his job.
Image copyright Getty Images Image caption Claude Puel has said he hopes his side can stay united after Mahrez's transfer falling through.
Despite a second transfer request from the player in eight months, Leicester reportedly held out for a deal worth 80 million ($113 million, 91 million euros), with even City's cash-rich Abu Dhabi owners unwilling to go beyond 60 million.
It's hard to forget how Leicester City won an unexpected Premier League title during the 2015-16 season, rising above enormous adversity, and showing grit and determination against the well established sides.
While credit has to go to Claudio Ranieri for masterminding such brilliant feat, it's impossible to underestimate Riyad Mahrez for his remarkable contribution to that famous success.
"One point is important because the history of Swansea at Leicester is very, very bad", he said after the match.
"All the staff, especially all the squad, they are his friends".