With Chelsea's first-choice left-back Ashley Cole unavailable for the first leg trip to the Camp Nou through suspension, coach Guus Hiddink must decided how to handle right-sided Argentine Messi, one the best players in the world, who is enjoying the best form of his career.
Primarily a centre-back or right-back, Mancienne played on the left of Chelsea's defence in Monday's reserve-team draw against West Bromwich Albion as Hiddink ran the rule over the England Under-21 international.
Aware that he could be asked to face Barcelona and Messi out-of-position, 21-year-old Londoner Mancienne insists he is ready to answer the club's call.
''It was a new one on me, I've never really played there before. I would love the challenge of facing Messi,'' Mancienne told Chelsea TV. ''The manager came to watch and I was asked to have a go. The manager is keeping his options open.
''They told me a couple of days ago I would have a go at left-back and I did ask Ashley a few questions about it. It felt all right.''
With Cole suspended, Jose Bosingwa injured and the versatile Branislav Ivanovic currently filling in at right-back, Chelsea are thought to have even considered asking Florent Malouda to restrict his attacking flair and deputise as a defender. But with the Frenchman seemingly rejuvenated on the left wing, limiting his impact on the game could prove counterproductive.
Other than opting for Mancienne, Hiddink's only other option would be to rely on Brazilian Julanio Belletti who also featured in Monday's 2-2 draw with West Brom.
The former Barcelona player is a right back by trade and so could replace Ivanovic allowing the Serbian to move into the troublesome left-back berth.
Hiddink's choice appears to be between playing the inexperienced, but lightening quick Mancienne or shuffling his pack to create space for Belletti who may not be 100% after returning from injury.