It is a strange old footballing March this in the city of Dundee.

For Dundee FC there are only two competitive fixtures to look forward to and none at all on a Saturday. A Wednesday meeting with Celtic on the 18th to be followed by Monday night football against Aberdeen on the 23rd.

Meanwhile, along the road at Tannadice, there is only one opposing team to be confronted, albeit they have three fixtures lined up with them.

Three meetings with Celtic in three different competitions at three different venues...

It is the unlikeliest of sequences in football terms, yet it brings to mind days of covering Test series in rugby with all the scope those have for analysis, over-analysis, surprises, bluffs and double bluffs.

That is what confronts these clubs over the next three weeks which will almost certainly define their respective campaigns.

It is all the more intriguing given the way their respective fortunes have been interwoven of late.

For United supporters the upset caused by the sale of Stuart Armstrong and Gary Mackay-Steven to a rival Scottish side which already boasted such superior resources and has the capacity to recruit while most, if not all domestic competitors must rely largely on development, has been greatly exacerbated by events since their departure.

Celtic may not have subsequently progressed in Europe, but those meetings with Inter Milan that evoked so many memories of the great feats achieved by homegrown Scottish players of yore allowed both former United players to demonstrate their capacity to shine at the highest level.

Meanwhile, looking at form and results, their old club appears to have gone into freefall.

United's loss of form has been such that it almost seems disproportionate given that, in the weeks before the dynamic duo left, there had been evidence of strength in depth within their squad which suggested the team might not perform quite as stylishly, but would remain highly competitive.

It is worth remembering that in the last match before they left Armstrong and Mackay-Steven played throughout, yet it was fellow midfielder Ryan Dow who was rightly credited by manager Jackie McNamara with turning that League Cup semi-final against Aberdeen with his energetic contribution off the bench.

A week before United were pretty lacklustre against a Motherwell side that had not won in weeks before teenager Charlie Telfer turned things their way with two high class goals.

Personally I was consequently quite surprised on turning up at Tannadice for their first home match since the big sale, to discover that neither Telfer nor Aidan Connolly, another bright young creative talent, were in the starting line-up and the directness with which United played against St Johnstone that day played into their visitors' hands.

In a reversal of the old adage about seeking to make the whole bigger than individual parts, the impact of the loss of Armstrong and Mackay-Steven seems to go beyond the loss of these two particular players and the extent to which what they contributed could be replaced or compensated.

The morale of players and, perhaps, management may have been affected by a decision that Stephen Thompson, the chairman, has admitted was problematic from a footballing perspective, but was also, he believed, necessary for business reasons and he has denied that it has caused a rift between board and team management.

We have surely seen enough in Scottish football these past two decades to understand that rationale, but the question now facing United is whether they still have what it takes within their club to recover and that is, in essence, what was originally meant when the word "Test" was coined to mark rugby and cricket battles at the highest level.

In Scottish terms a trio of matches that will go a long way towards deciding whether Celtic will win a treble this season represents exactly that carrying, as it does, the potential to have the same ebb and flow we often see in Test series'.

Both obviously go into Sunday's Scottish Cup tie hoping they can win all three matches and the winners will immediately be established as favourites to go on and win that tournament. For the losers the winner-take-all meeting the following week will take on added significance.

Naturally Celtic are odds-on favourites to win them all but Test series' are relatively rarely won 3-0 and United should have the personnel to produce at least one upset, albeit they will hope it is not a consolation one in the league game at the end.

Whatever happens, though, Thompson is set to find out a great deal about the capacity of his managerial team to inspire and motivate in adverse circumstances and the courage of his front-line troops.

It promises to be a fascinating series of encounters.