JOHN SOUTTAR has challenged Rangers to make amends for their 'unacceptable' loss to Aberdeen by seeing off Celtic in the Scottish Cup.

Michael Beale suffered the second Premiership defeat of his reign on Sunday as the Dons continued their terrific run under the guidance of caretaker boss Barry Robson.

Liam Scales scored a hugely fortuitous opener at Pittodrie as he beat keeper Allan McGregor with a speculative cross from midway inside the Rangers half.

But the defending for the crucial second goal left much to be desired for boss Beale as Bojan Miovski was left unmarked to head home at the back post.

READ MORE: Michael Beale makes Rangers 'warning sign' call after Aberdeen loss

Rangers have little time to regroup and recover from the shock loss as all attentions turn to the Old Firm showdown at Hampden this weekend.

The winner on derby day will be huge favourites to go on and lift the silverware this term and Souttar knows Beale's side must show the right reaction on the back of a poor Pittodrie performance.

“It was a tough 90 minutes for us," Souttar told RangersTV. “We have got beat 2-0 at the end of the day and can say all we want but we left with no points and that’s unacceptable.

“We’ll need to look back and see what went wrong. Obviously the first goal they scored was a freak goal but with the second one I think we can do better.

“It just can’t happen, we can’t get beat 2-0. We need to make it better.

“We now have got to lift ourselves massively. It’s a big game on Sunday, a massive game, so we need to pick ourselves up and not feel sorry for ourselves. We need to get ready for Sunday and get through to the final.

READ MORE: Barry Robson reveals referee ball boy call as Aberdeen beat Rangers

“It just makes it extremely difficult when you lose goals like we did at Pittodrie, it makes it extremely difficult. We saw it at the start of the season but managed to come back late on.

“That’s something you don’t want to have to do as a defender, you want to keep clean sheets. So co concede goals like we did is extremely frustrating.”