Lb is much more of a problem. Bellerin is as reliable as it gets and AMN is very good back up.
How is LB more of a problem? Monreal is still playing at a high level, he's not ready for the retirement home just yet. Kolasinac is young and adapting, plus AMN can fill in there. I mean I'd trust AMN to fill in at RB too, but shouldn't we have more than one designated RB?
Fabinho would be a handy solution to this problem I guess. Fabinho plays at DM and Bellerin at RB, if Bellerin gets injured Fabinho slots in at RB and AMN at DM or AMN at RB.