Rangers are flying in the Europa League, but they have already dropped 12 points in the league and lost to Aberdeen in the cup semi-final last weekend. Jack is calling for unity.
"The players on the pitch have to take responsibility," the midfielder said.
"We can’t be saying: 'Oh, it’s this, it’s that,' and making excuses. It’s us who are on the pitch. It’s us who cross the white line to go on and do the business.
"We have a lot of experienced players, a lot of players that have their say and a lot of players who have been at the club before.
"There is a lot of experience in the squad, so it’s important we knuckle down and stick together."