Manchester United eased into the last 16 of the Europa League with a 1-0 victory at Saint-Etienne, winning the tie 4-0 on aggregate.

However, manager Jose Mourinho will no doubt be concerned by an injury to goalscorer Henrikh Mkhitaryan, who could now miss Sunday's EFL Cup final after limping off.

United started very well and Mkhitaryan gave his team the lead after smartly flicking in Juan Mata's cross after just 16 minutes. He left the pitch clutching his hamstring minutes later.

Eric Bailly was then sent off for two bookable offences in the second-half, but United rarely looked under pressure and saw out a comfortable 1-0 away win.

Here are five things we learned from their routine victory...

Mourinho is taking the Europa League seriously

Mourinho picked a strong team (Getty)

With the EFL Cup final against Southampton kicking off on Sunday, and with the club still fighting for a Champions League spot in the Premier League as well as in the FA Cup, many had expected Jose Mourinho to field a weakened team in the second-leg of this Europa League clash.

After all, Manchester United had seemingly all but confirmed their progression to the Round of 16 stage when they swept Saint-Étienne aside 3-0 at Old Trafford.

So eyebrows were raised when Mourinho’s team-sheet was revealed an hour ahead of kick-off. A virtually full-strength team – with the exception of Sergio Romero replacing David de Gea in goal – was named, with Paul Pogba, Henrikh Mkhitaryan and Zlatan Ibrahimovic all selected.

In choosing such a strong XI, Mourinho sent out a clear message: he is taking the Europa League as seriously as he would the Champions League. Unlike Tottenham Hotspur, who looked below par and uninterested in a defeat to Gent last week, United started this match at a fierce tempo and surely have to be considered among the favourites for the competition, which concludes in Sweden at the end of May.

But naming such a strong team was a big risk

Mkhitaryan was forced off in the first-half (Getty)

The downside of Mourinho selecting such a strong team was the potential injury-risk. And it wasn't long before he was forced into making an early substitution, when Henrikh Mkhitaryan appeared to tweak his hamstring after racing with Kévin Malcuit for the ball.

Given the superb form of the Armenian international in recent weeks, United will very much hope his injury is not a serious one: Mkhitaryan has been involved in 5 goals in his last 6 games for United in all competitions (3 goals, 2 assists). Fortunately, the early indications coming out of the club were that the substitution was a precautionary decision.

But it is testament to United's strength in depth that the injury did not effect United's performance on the night. Rashford came off the bench in a like for like substitution and immediately set to work running hard at the Saint-Étienne defence.

But a later injury to Michael Carrick, as well as Eric Bailly's rather harsh red-card, will test United's strength in depth even further. Mourinho's decision to name such a strong starting XI was always going to be a risk and only time will tell if it is one that paid off.

Ibrahimovic deserves better service

Ibrahimovic was loudly booed every time he touched the ball (Getty)

Zlatan Ibrahimovic has scored 17 goals in his last 14 matches against Saint-Etienne and is so reviled in this part of France that he is known as the 'Scourge of Saint-Etienne'.

He failed to add to that formidable tally this evening, but that was hardly his fault. Ibrahimovic was at his typical boisterous best, causing confusion in the Saint-Etienne back-line with his smart running and frequently drifting out wide to link up with his team-mates, but lacked adequate service.

He stood completely unmarked early in the second-half only for Fellaini to attempt an ambitious shot from an acute angle when he could — and should — have just squared the ball. And, towards the end of the game, Daley Blind's cutback was poorly placed which allowed Loïc Perrin to clear whilst Ibrahimovic again stood unmarked.

As the final whistle blew, Ibrahimovic cut a frustrated figure, fully aware that had his team-mates been on form, he would have scored his 18th goal against the French side. He will have to hope that they up their form at Wembley.

It’s hard to see how Rooney fits into this United team

Rooney was left out of Mourinho's matchday squad (Getty Images)

After a slightly faltering start to his Manchester United tenure, Mourinho looks to have finally settled on his strongest XI – and it’s difficult to see how Rooney fits into it.

Zlatan Ibrahimovic is simply undroppable up-front. Behind him, a revitalised Henrikh Mkhitaryan opened the scoring before his early injury and Mata was lively, assisting the first goal and creating a number of good chances.

Paul Pogba looked powerful nudged into a slightly advanced role and Marcus Rashford terrorised Kévin Malcuit with his direct running in the second-half.

When you factor in that United also had Anthony Martial and Jesse Lingard on the bench, it becomes increasingly hard to work out where Rooney's chances are going to come in the second-half of this season. He may not want to move to China in the next seven days, but it's unlikely he's going to be given a chance to impress if he stays in Manchester.

Ligue 1 is a growing force in European football

There was a raucous atmosphere at the Stade Geoffroy-Guichard (Getty)

Saint-Étienne are fifth in Ligue 1, a league generally considered to be lagging behind the Premier League, La Liga, the Bundesliga and Serie A when it comes to the strength of its teams and the quality of its football.

And yet Mourinho still saw fit to field his strongest team for this encounter. United won this match relatively comfortably and the outcome of this tie was never in doubt after their 3-0 win at Old Trafford, but Saint-Étienne gave a good account of themselves and players such as Saivet, Veretout and Malcuit all impressed.

On Tuesday AS Monaco were superb going forward in their heroic 5-3 Champions League defeat to Manchester City and PSG's stunning 4-0 victory over Barcelona last week dominated headlines across Europe.