Rangers captain Lee Wallace will miss Tuesday's League Cup quarter-final against Partick Thistle and Saturday's Old Firm derby because of injury.
The left-back went off with a groin knock during his side's 2-2 draw with Partick Thistle on Friday night.
"He is travelling to Manchester today to have an assessment on his groin so let's see how it goes," manager Pedro Caixinha told the club website.
"He will miss the weekend, we just need to know how long he needs to be out."
Summer loan signing from Cardiff City Declan John came on for Wallace in Friday's Premiership match at Firhill, and while he complained of an "ankle niggle" afterwards, Caixinha added: "Declan John will definitely be with us tomorrow [Tuesday, against Partick], as will Ryan Jack, who will start.
"He didn't play that much with Cardiff City so he's a little bit out of rhythm but he is one player that we trust totally.
"He is going to give us different things than Lee would because they have different characteristics, even though they play in the same position.
"He has all our confidence and for sure he is going to be on the pitch and have a very good game.
"If he cannot play [on Saturday] we still have an option but I am not going to guess what's going to happen on Saturday before things happen on Tuesday. Now he is ready to play and after he will have four days to recover. Then we will have time to decide.
"It's always a disappointment when you lose players.
"I would like to have everyone fit and besides that Lee is our captain. At the moment he is heading to Manchester to be assessed and we will see how much time he is going to be out."
Jack had to be treated following a tough challenge by Thistle's Ryan Edwards, but the midfielder continued until later in the second half.
Caixinha also revealed the club are assessing Niko Kranjcar, who has picked up a knock on the same knee he injured last season, while Jordan Rossiter is also out because of a knee complaint.
The Ibrox boss confirmed Kenny Miller will be rested for Tuesday's match against Thistle.