Summer signing Nnamdi Ofoborh is being sent to a specialist by Rangers after "a heart issue" was revealed by a scan following his switch from Bournemouth.
The 21-year-old midfielder moved to the Scottish champions after ending last season on loan to Wycombe Wanderers.
Manager Steven Gerrard explained why he did not feature in Saturday's 2-2 friendly draw against Arsenal.
"Unfortunately, something's flagged up on his ECG, which is the heart tests," he told Rangers TV.
"I don't think you'll see him in the short term. It's frustrating, but we'll have to manage and cope. The important thing is the player's health, which we'll focus on first and foremost."
Ofoborh initially agreed to join Rangers in January and started a four-year deal with the Scottish Premiership club when his Bournemouth contract ended this summer.
"We've got top medical people here at the club now and we check all the players from head to toe when they arrive," Gerrard added.
"Unfortunately, there's been a bit of a red flag with a heart issue, so he's going to see some specialists in the coming weeks and we need to do more tests and checks.
"Of course it's disappointing and frustrating for the player, but I spoke to him yesterday and I told him to keep smiling and be patient and we'll do everything we can to support him, get him in front of the right people to give him the right support and hopefully he'll be back before not too long."