Walter Smith insists his players have to remain focused to have a chance of winning the domestic treble this season.
The Rangers boss watched his side squander a two-goal lead in Sunday's 3-3 draw with Dundee United in the Active Nation Scottish Cup quarter-final.
Smith, whose team are 13 points clear of Celtic at the top of the Clydesdale Bank Premier League and face St Mirren in Sunday's Co-operative Insurance Cup final at Hampden, warned: "What happened against United is something that worries me, for the simple reason that everyone is saying we're on for a treble, and that is premature."
He added: "It's the first time I've seen my team relax in that manner and allow the opposition to come back.
"Once we scored the third goal there was a slackness that came into our play. That slackness is unusual for our boys. They've been fantastic in their approach.
"I think a bit of complacency could come in because the expectation is that, with this points gap in the championship, people say you've won the league.
"So this sends out a message to everybody that we won't achieve unless we remain fully focused on what we have to do.
"We have a cup final to play on Sunday. But we have a whole load of cup finals to play if we are going to succeed this season.
"I know everyone is saying I'm just playing at it when I say that, but this shows that it's not the case. I'm making a realistic appraisal of what we have to do between now and the end of the season if we are going to succeed.
"We now find ourselves in a really tough replay at Tannadice, and we might still have to go there twice in the championship."
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