The Bayern Munich man has been linked with Barcelona for some time now, and according to Albert Garcia of Catalan outlet Sport, Madrid tried their luck during the summer: "Madrid have had Alaba in mind for a while, trying in the summer but unable to convince the Bavarians to sell."
Per the report, Alaba's versatility is key to Zidane's interest. A wave of defensive injuries has hit Los Blancos, and the absence of the likes of Marcelo, Dani Carvajal and Theo Hernandez has highlighted the lack of depth.
The Austria international made his name as a full-back but has also played as a centre-back and in midfield. His excellent all-round game means he regularly contributes in front of goal, as you can see in this video:
The 25-year-old from Vienna has spent his entire professional career on the books at Bayern, apart from a loan spell at Hoffenheim. While links with La Liga have been persistent, it seems likely he'll stay in Germany, where he's relatively close to his hometown.
Alaba has a tremendous reputation as one of the world's best full-backs, although he has struggled for consistency of late. Casual fans still rely on his reputation, but the Bavarian faithful have spoken openly about his need to improve.
Per TheBayernFanTV, manager Jupp Heynckes has also discussed his poor form:
The timing of these rumours certainly seems odd―if Madrid had an interest in the player, it likely would have come at a time when he was at his best. It is possible Los Blancos believe he can rediscover his best form with a change of scenery, however.
Even if he's not at his best, Alaba's versatility still makes him an interesting target. While he's not a great fit in a central role as a part of a defensive duo, he held his own in a three-man back line in the past―it's a formation Madrid have yet to test but could add to their arsenal.
His best position remains left-back, however, where Madrid field arguably the best in the world in Marcelo. It's hard to see any scenario in which the two coexist or the Brazilian is benched in favour of Alaba.
The Austrian is highly unlikely to leave Bavaria for a rotational role―if Alaba does end up leaving, it will be to be a starter elsewhere.