According to Mundo Deportivo (h/t Jack Stewart of the MailOnline), Barcelona boss Ernesto Valverde is concerned about the lack of depth in the position, as Alba is the only senior option in the squad. That's after the La Liga side sold Lucas Digne to Everton this summer.
As such, they are said to be looking at both Monreal and Moreno. The duo may be available for cut-price amounts in January or on a free transfer after the season, as their contracts are set to expire at the end of 2018-19.
It's also suggested in the report that Barcelona are keeping an eye on Atletico Madrid left-back Filipe Luis. Speaking to Globoesporte (h/t Robin Bairner of Goal), the Brazilian said he asked for a move to Paris Saint-Germain this summer.
After letting Digne move on, the Blaugrana are set to hand Alba a heavy workload this term, something that's far from ideal for the 29-year-old if he is to stay fit for the duration of the campaign.
However, he was left out of the recent Spain squad, meaning it's less likely he'll have international commitments to fulfil. Rafael Hernandez of Grup 14 believes that should help Alba ensure he's at his best for the Camp Nou side:
Even so, injuries and suspensions are inevitable, and if Alba were to miss a sustained spell of matches suddenly, the Blaugrana would look a little short in this area.
Monreal would be a savvy option, especially given he has played in La Liga previously, enjoying spells with Osasuna and Villarreal before making the switch to Arsenal. While he's not as dynamic as someone like Alba, he's an intelligent, versatile footballer that's become a key man for the Gunners.
The Spaniard has also developed a reputation for chipping in with some important goals for the team:
Moreno has found himself down in the pecking order at Anfield following the development of Andy Robertson and would surely benefit from a move. However, at this stage in his career, the former Sevilla man will be desperate for regular minutes, which is not something he'd be guaranteed at Barca.
Although there are major holes in the Liverpool man's game defensively, he can offer a major threat going forward, and in the main that's what his job would be in a setup like Barcelona's.
Still, Blaugrana supporters would potentially want someone younger who can eventually challenge Alba for the starting spot as he moves into his 30s. Neither Monreal nor Moreno appear capable of being anything other than a deputy.