Nancy, Ayunga & Hearts v Rangers in spotlight

Another tumultuous week in Scottish football climaxes with a weekend of increasingly important Premiership games at both ends of the table.

Premier Sports Cup winners St Mirren return to league business at home to beleaguered bottom side Livingston in one of four Saturday fixtures.

But the big ones at the top are on Sunday as leaders Heart of Midlothian entertain Rangers, while Aberdeen visit a Celtic side in turmoil after Hampden disappointment was followed by a loss to Dundee United that consigned new manager Wilfried Nancy to an unprecedented fourth defeat in a row.

Here are some key things to look out for.

Just when it looked like Hearts' surprise title challenge was faltering, they have followed up four games without a win with two straight victories.

Combined with Celtic's sudden four-game losing streak under Nancy, albeit only two in the league, Derek McInnes' side are six points ahead of the reigning champions again.

Rangers are now only three points further back thanks to their two rivals' recent stumbles and a steadying of the Ibrox ship under their new head coach, Danny Rohl.

That makes Sunday's meeting at Tynecastle all the more significant for both their seasons.

Hearts' 2-0 win at Ibrox in September played a part in Russell Martin's Rangers reign ending after just 17 games - as well as cementing the Edinburgh side as potential challengers at the top of the table.

Having also beaten Celtic twice, becoming the first non-Old Firm side to win four consecutive top-flight meetings with the Glasgow duo since Dundee in 1985 would further strengthen their case, especially as it would widen the gap to third to 12 points.

Despite that tough run of November fixtures, Hearts have only lost once in 15 outings and remain unbeaten in 11 games at home, nine this season.

Like Hearts, Rangers under Rohl have managed to avoid defeats despite struggling to produce fluid performances.

The Glasgow side have themselves only lost once in eight outings and remain unbeaten in 19 away games in the league since defeat by St Mirren on Boxing Day last year.

Avoid defeat again on Sunday and it will be the seventh time in their history that Rangers have completed a calendar year without a league reverse on the road.

They head to Tynecastle unbeaten there in eight visits, winning six of them, since a 2-1 loss in January 2020.

Despite Rangers' deficiencies, Hearts remain the only side to have beaten them in the league this season.

Repeat their 3-1 win there on their latest visit in February and a three-way title race would very much be on again.

Given there will have been a bit of partying going on in Paisley since Sunday's win over Celtic at Hampden, St Mirren will probably be relieved that their next opponents are bottom-placed Livingston - and in front of their own fans.

There is likely to be a party atmosphere at SMiSA Stadium and Jonah Ayunga will hope to be swept along to another goalscoring performance after his brace in the League Cup final.

Indeed, the 28-year-old England-born Kenya striker has three goals in his latest three appearances.

Should he score in back-to-back matches for St Mirren for the first time, he will match his goals tally for the previous 42 games.

Given Livingston have not won in 15 outings and have not won in their latest nine visits to Paisley, albeit only losing five, Stephen Robinson's ninth-placed side will be confident of a victory that is much needed considering they are in danger of being one of four sides detached at the bottom.

Especially so since David Martindale's side have just one league win this season, the fewest by any side in their opening 16 matches of a Scottish top-flight campaign since Gretna also started with just one victory in 2007.

Latest indications are that Nancy will still be Celtic manager when Aberdeen arrive in the east end of Glasgow come Sunday.

Whether or not he remains so could depend on whether they end the dismal four-game losing run since the Frenchman replaced interim manager Martin O'Neill.

Chief executive Michael Nicholson claimed that three staff members were assaulted after Sunday's League Cup final defeat, then it was announced that Peter Lawwell is standing down as chairman because of "abuse and threats" from disgruntled fans.

Celtic's latest four days of turmoil were topped off by the concession of an early lead as Nancy's side lost 2-1 away to Dundee United on Wednesday.

It might seem a bit unfair after just four games, but considering he has lost twice more since becoming the first Celtic manager ever to lose his opening two in charge, it is little surprise there was speculation that at least some of the board already want to end Nancy's tenure.

He is also the first Celtic manager to lose four games in a row since 1978.

Nancy can point to the fact the legendary Jock Stein was in charge at the time as proof that even the best can recover from such adversity, but the Celtic support are unlikely to be so forgiving unless the run ends on Sunday.

Lose again and it will be only the third time, and first since April 1953, that Celtic will have suffered five in a row.

Aberdeen arrive having earned more points than any other side in the Premiership since the start of October, winning seven and losing just one of their league games - and only losing twice in 11 overall.

However, Jimmy Thelin's side are fresh from another bruising European defeat, 3-0 away to Sparta Prague, meant they finished second bottom of the Conference League as a four-game unbeaten run away from home came to an abrupt halt.

Nancy also has history in his favour, Celtic remaining unbeaten against the Dons in 32 meetings, winning 25 of them, since Aberdeen last won at Celtic Park in May 2018.

Since then, they have lost 10 of 12 visits, but much has changed since Brendan Rodgers led Celtic to a 2-0 win in the reverse fixture in August, with Aberdeen moving up to sixth and within five points of third-placed Rangers.

Thelin had his own shaky start as his preferred formation was initially found wanting in Scottish football.

Nancy, though, looks determined to stick with his change to three at the back rather than the four that served O'Neill well during seven wins in eight outings in interim charge.

It has left Celtic looking more vulnerable at the back, but Sunday's result could have as much to do with which side can take the many chances being created at the other end as they have the two biggest negative xG differences of any sides in Scotland's top tier this season.

Celtic have scored 26 goals from 33.5 expected goals (an underperformance of -7.5) while Aberdeen have scored 18 goals from 22.1 xG (an underperformance of -4.1).