Celtic continue their domestic treble quest when they face Dundee in the Scottish Cup fifth round on Saturday just as Old Firm rivals Rangers appear to be imploding.

The Hoops currently top the Scottish Premiership and cruised into the League Cup final following last weekend's 2-0 defeat of Rangers at Hampden.

One player who knows all about Dundee is striker Leigh Griffiths who scored 34 goals for the Dens Park side in 62 appearances between 2009 and 2011.

And the forward, who headed home the opener in last week's Old Firm fixture, is keen to help fire his side to another cup victory.

"It's a massive game for us because we want to win the competition," the Scotland international said.

"Dundee will be looking at the last round and how they beat Aberdeen, perhaps thinking that they can then do the same to us but, we have to go up there with the right attitude, play the right way, dominate the game and hopefully that's going to be enough to take us through.

"It will be a difficult game. We went there last time and dropped two points and we were lucky to come away with a point because the chances they had with 10-15 minutes to go really should have buried us and put us out of sight.

"Dundee were tipped for relegation at the start of the season but Paul Hartley has come in and done really well.

"They had a great start to the season and then hit a little bit of a sticky patch, but they have picked up their results recently and they beat Aberdeen in the last round of the Scottish Cup, so they will be looking forward to the game and they will be aiming to take another scalp at home."

Ronny Deila, who is looking to become only the third Celtic manager in the club's history to win a clean sweep of domestic trophies, was handed a boost when Kris Commons signed a new two-year contract.

Meanwhile, Rangers have been forced to deny claims from caretaker manager Kenny McDowall that he must select the loan signings the club have made from Newcastle United.

Midfielders Gael Bigirimana and Haris Vuckic and defenders Kevin Mbabu, Remie Streete and Shane Ferguson joined from the English Premier League side on transfer deadline day.

Speaking ahead of his side's cup tie against Raith Rovers at Ibrox on Sunday, McDowall said he had been told by chief executive Derek Llambias and director Sandy Easdale that the quintet must play if fit.

However, Llambias, who was formerly chief executive at Newcastle -- owned by Rangers shareholder Mike Ashley -- disputed McDowall's claims.

"There's no way the board is picking the team," the Rangers chief executive said.

"In any loan the players bolster the side and give the squad more depth. That's exactly what is happening here."

Elsewhere on Saturday, there is an all Premiership encounter between Partick Thistle and Inverness Caledonian Thistle, non-league Spartans FC host Berwick Rangers, Queen of the South take on holders St Johnstone and Hibernian face Arbroath.

Last year's beaten finalists Dundee United are away to Stranraer on Sunday.

Fixtures (1500GMT unless otherwise stated)