Philippe Clement revealed illness has prevented Vaclav Cerny being involved for Rangers against Dundee United this afternoon.
Cerny, 26, has been a mainstay in the Light Blues' team since arriving on-loan from Wolfsburg over the summer.
He was expected to be involved from the off again today, however the Czech winger took ill during a recent training session, with a decision made to leave him at home.
Kieran Dowell replaces him in the starting XI.
Speaking to reporters before the match, Clement said: "Cerny was normally a starter. So he trained yesterday but he felt not so good during training suddenly and then in the afternoon he became really ill. He had to vomit several times so he felt very bad this morning.
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"He's ill, it's not an injury or something, but because of that, Kieran Dowell comes into the team.
"Oscar is getting back after a long injury, so week after week he's becoming better, and it was a good moment to give him a start now and it's the next step in the process for him to become the player he was before.
Clement was expecting a tough test at Tannadice as he looks to guide Rangers back to winning ways.
"Every game will be massive all season," he told BBC Scotland. "That's what Rangers is all about - you have to win almost every game if you separate the league from Europe.
"It is a big opponent. They have a really good dynamic by winning promotion and making a really good start to the league.
"So, on a small pitch with a lot of duels, it is going to be a very tough game."
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