With Smalling it is likely that he will start in the heart of the defense of Ole Gunnar Solskjaer and Messi intent on interpreting the role immortalized by his unparalleled phenomenon, the couple – at first sight from the game – will be well informed. Leaving Messi unattended is, at best, imprudent.
Mikael Silvestre – a winner of the Champions League during his time at Manchester United – has recognized that it is the divine splendor of Messi who stands in his old team on his way to an unlikely semifinal place.
"Barcelona – except" Dio "(Messi) – it's a team you can stop in two games," Silvestre told CNN Sport last month. "I think United can stop Barcelona and progress."
Given both the style of play on the Catalan side and the central importance of Messi, Silvestre is well aware of the determination and luck needed if his former club has to stay in the game long enough to interest the five times winners.
"They did it against Paris [in the previous round, where United overcame a 2-0 first-leg deficit to win on away goals]. They ended up playing with Mason Greenwood, Tahith Chong, James Garner – the three young men – in the Parc des Princes.
"It was a stimulating performance, with that mental capacity to remain in the game and to believe and never give up, it is in the DNA of the club – that attitude that never gives up".
Messi, even if it remains the key. As a defender who collected 249 appearances during Alex Ferguson's, Silvestre has a warning for his former team.
"It is when you have the ball that it is more dangerous because it is about to disappear and then reappears," explained Silvestre of Messi's threat.
"[Stopping him] It was done before, "he points out." We know how to do it. "In fact, Silvestre himself succeeded: he entered as a late substitute when England beat Barcelona with only one goal in the 2008 semi-final.
More than a decade later, Messi's icon has stood the test of time. That the Argentine has not been crowned as the greatest player in the world since winning its fifth Ballon d 'Orno title in 2015 is, in many ways, a false track.
His unique ability never declined, nor his numbers; 26 goals in the 2015/16 La Liga season were subsequently followed by 37 and 34, with the great Argentinian seated at the 33rd with seven games of the current season remaining – a year dominated by his Barcelona team.
In this year's Champions League, Messi's six appearances have brought eight goals and three other assists with them.
It is a race that has added to an already outstanding overall record in Europe's biggest club competition; 108 goals in 131 appearances give him a score of minutes per goal higher than that of his great rival Cristiano Ronaldo, although the Argentine remains 16 rounds behind Juventus 124 ahead.
The duo's long battle for football supremacy saw them compete in a competition of its own. The former Real Madrid captain, Raul Gonzalez, is the closest challenger to the pair, but his 71 goals also put him behind Messi.
Of those still active, Karim Benzema is the next closest, but his 60-point Champions League loot is less than half of Ronaldo's astronomical figure.
Alongside Messi's extraordinary timeless supremacy, however, she was accused of having struggled to reach her own high standards in the face of the English opposition.
Yet, for almost as long as the theory existed, it is a label that Messi confused. There are, of course, occasional outliers. Messi's record against Chelsea, for example, is only three goals in 10 games.
However, his story with Manchester United is different. Although he currently only shows two goals in four games, those strikes arrived in the finals of 2009 and 2011. His performance at Wembley in the second of the two is remembered for his majesty, while Barcelona won the victory by 3 -1.
Some hope, perhaps, for the faithful of the Old Trafford comes to Messi's record on English soil.
Despite a famine for goals, Messi has played eight times in 15 games in England, against 13 games in 14 at the Camp Nou. Indeed, it is also without a goal in his last 11 Champions League quarter-finals.
It remains to be seen if this is an omen for the Solskjaer part – good or bad.