Finally confirmed out for the season after a day filled with rumors, it's incredibly hard to forecast what Liverpool will do without Lucas. He's missed just three of Dalglish's 39 matches: rested for two, suspended for one. Since 2009, he's missed so few games that it's statistically irrelevant posting win-loss percentages with and without the player: he appeared in 34 of 38 league games in '10-11 and 35 of 38 in '09-10. Incidentally, he's never missed a Liverpool game through injury. Until now.
Considering the three missed under Dalglish, Exeter in the Carling Cup barely counts, so we're left with this season's 1-1 v Norwich and last season's 1-0 v Fulham. The former saw Liverpool stick with the primary 4-2-2-2 formation with Gerrard and Adam in midfield. With Liverpool's captain still out indefinitely, that's an unlikely template. The latter, early in Dalglish's reign, saw a 4-2-3-1 with Gerrard and Poulsen holding behind Meireles – also a poor template with both Meireles and Poulsen gone and Gerrard still injured. Liverpool impressed in neither.
There seem to be two options, at least until the January window when Liverpool will probably reinforce. One, stick with the 4-2-2-2 formation with Spearing or Henderson instead: the former more a like-for-like replacement, the latter probably adding more to the attack (which would require more defense out of Adam and, to be fair, he's been better in that regard lately). Or Liverpool could shift to a 4-2-3-1/4-2-1-3 as the primary formation, with both Spearing and Henderson included.
Either way, it's as big a loss as possible. Only Suarez and Reina are arguably more important to the side. I'm tempted to suggest that the three-man midfield is a better option, using a trio to try to cover Lucas' one-man band, but Dalglish has shown a distinct preference for the former formation this season. I expect Spearing will be given the nod in the 4-2-2-2 for Liverpool's trip to Fulham on Monday. Lucas' defense, his tackling and positioning, will be dearly missed, but Spearing's shown he can replicate that. It's the metronomic control over midfield, a calm head under pressure, settling and starting Liverpool's attacks, which will be the hardest to replace.
There are also a couple of more remote possibilities: Aurelio's covered in midfield before, while Liverpool could play three at the back, but neither seems incredibly likely.
Trying to sap the frightening emotion from this development, it'll be interesting to see how Liverpool cope. More often than not, Dalglish and Clarke have done excellently on the tactical front. This might be their biggest challenge yet. Yes, bigger than settling the ship last season, coping with the loss of the captain, or dealing with the exit of the former star striker. Interesting and terrifying.
Good luck, Lucas.