To me it seems Allegri considers Claudio to be a 2nd hand option, during the last month Claudio sat out both Spurs games, Torino derby and Lazio game, but played Udinese at home and Coppa return leg against Atalanta.
His competition for Pjanič position Bentancur has been riding the bench like crazy, so I think it's safe to say that Marchisio will play in CL knockouts in place of Pjanič if fit, but I highly doubt we're going to see Matuidi-Marchisio-Pjanič midfield, Khedira is still well ahead of him in the pecking order and March is a tough month to change this, Claudio would need to hit serious form to get the nod.