Liverpool's depth at fullback over the years has been a major problem. Injuries can be blamed, no doubt, but on some level the club are accountable for failing to provide adequate cover for positions that have had extended layoff for each of the "regulars" in the past five seasons. This season is the same as the others--both starters on either side out for long spells, players placed out of position to cover, backups proving too young or too ineffective to be relied upon with any sort of consistency.
And while it's great that Glen Johnson is back in the starting lineup, it's simultaneously unsurprising that Jose Enrique won't be, or that many are concerned about Aly Cissokho playing regularly in Enrique's absence, or that there's a decent argument to be made that Jordan Henderson could be one Liverpool's best options as cover despite being their most effective midfielder to this point in the season. There's Martin Kelly too, though he's been off the pace since returning from injury, and, as we saw against Arsenal--or didn't see for at least one Liverpool supporter--Jon Flanagan is an option as well.
That caused much consternation among those who did watch as well, though the young defender performed admirably, and his manager views that as part of overall improvements that now have him placed as a potential replacement for the injured Spaniard:
"With Jose out, I've got Aly Cissokho, who came in as cover, but I've also got other options like young Jon Flanagan. Jon has been outstanding in training and he seems to be getting better and better. He did very well against Arsenal. He didn't do anything wrong in that game. When he came off, it was simply because we wanted to be more offensive as we were chasing the game. Jon is a young player who will never let you down. Of course it's disappointing if you lose your No.1 left-back but it's an opportunity for someone else to come in and do well. I'm not concerned about that position. Cissokho and Flanagan can both play there."
That can be read as an indictment of Cissokho's play (and it should be, though it ignores Johnson's impressive cameo on the left last season), but it's also an indictment of Liverpool's failures to account for what's been a consistent pattern in the last few seasons. Fullback is good, fullback is hurt, PANIC!!!1!!
So it turns out that more than one fullback that's ready in terms of both fitness and quality for consistent first-team football would be a good idea. Competition would be a bonus, as would the hand-wringing over which fully fit and on-form fullback should be getting the start. Instead of, you know, trying to figure out which central defender should play as a fullback or which midfielder would do least worst or which young player the club are going to offer up as sacrifice.
If Jon Flanagan starts, it'll be because he deserves it given his hard work and solid display against Arsenal. And in the unfortunate event that he struggles and leaves the side looking exposed, overmatched, and lacking in quality depth, it'll be because Liverpool deserve it.