Manchester United are keeping an eye on Barcelona left-back Jordi Alba with a view to a possible summer move. 

That's according to Rob Dawson of the Manchester Evening News, who added there are doubts over the long-term future of Luke Shaw at Old Trafford.

It’s noted in the piece that Alba has been left out of the Barca side for key matches recently, with manager Luis Enrique shifting to a 3-4-3 setup. "And there has been speculation in Spain the 28-year-old has become unsettled," with the Red Devils said to be admirers.

Alba will now reportedly "wait to discover the identity of the next coach before making a decision" on his future. Manchester City are also said to be interested in the £25 million-rated Spaniard.

Although Alba has been rotated in and out of the Barcelona team lately, he is considered to be one of the best full-backs in world football. Here's a look at what he can offer:

The 28-year-old has been a blistering presence on the left flank since moving from Valencia to the Camp Nou in 2012.

Alba is one of the most adventurous left-backs in the game. With Neymar drifting infield frequently from that side, space consistently opens up for Alba, who is so often found by Lionel Messi with passes over the top of the defence.

When he does get in those positions, the left-back is a threat. Down the years he's supplied many assists, as well as chipping in with the odd goal.

It would be an exciting acquisition for United, although Shaw's situation at Old Trafford is one that will be worrying those tied to the Red Devils. Per Oliver Kay of The Times, he's barely been seen in the top flight as of late:

Indeed, for a player who was considered by many to be the future of United and England, Shaw's stock has fallen dramatically.

The catalyst for that was a serious injury suffered at the start of the previous campaign, consigning him to an eight-month stint on the sidelines. Since his return to fitness, he's been unable to rediscover his best form and clearly hasn't impressed manager Jose Mourinho.

According to Dawson, the United boss recently deemed it "out of the question" that the 21-year-old would leave the club. BT Sport's Ian Darke can see why he may want a fresh start:

Although Alba's form for the Blaugrana has tailed off over the past 18 months, he would be a major asset for United in what has become something of a problem position. Not only would he give the team energy and incision on the left, the Barcelona man has been part of winning sides at both club and international level. 

If he did arrive, it would be bad news for Shaw, as Alba would undoubtedly take over as the regular left-back at Old Trafford. The England international, subsequently, must show Mourinho he has what it takes to become a mainstay of this side from next season.