Competition favourites Barca are locked at 2-2 against Paris St Germain as they head into Wednesday's second leg in Catalonia.
Messi is continuing his recovery from a thigh injury and will undergo a further test on Monday to assess his condition.
The Argentine has been enduring a course of physiotherapy since last Tuesday, when he injured his right thigh during the first half of Barcelona’s Champions League quarter-final clash with Paris Saint-Germain. Messi is understood to be set for another ultrasound to assess the condition of his injury. He will again be tested on Tuesday morning, when a decision on whether or not to include him in the matchday squad for Wednesday’s second leg against PSG will be taken.
The goals and magic of World Player of the Year Messi would usually be enough to dig Barca out of any sticky situation - as they did against AC Milan in the previous round - but if the Argentine does not play the team will need a different approach.
Messi sat out Saturday's 5-0 win at home to Real Mallorca in La Liga with a hamstring problem, the first league game he has missed through injury since the 2010-11 season.
Barca, though, still have reason for optimism that they can reach a sixth successive Champions League semi-final as Messi's stand-in against Mallorca, Cesc Fabregas, netted a hat-trick and coach Tito Vilanova was back on the bench after cancer treatment.
They are in good spirits after the return to competitive action of defender Eric Abidal following a liver transplant, while they remain 13 points clear of Real at the top of La Liga and have not lost at home in Europe for more than three years.
"There is life beyond Messi," Barca wrote on their website. "Maybe it's not as beautiful, but it exists."
Qatari-backed PSG geared up for the Barca trip by fielding a largely reserve team in a 2-0 win at Stade Rennes that restored a seven-point lead at the top of Ligue 1.
Brazil centre-back Thiago Silva is a doubt because of a knee injury he sustained in the first leg, while holding midfielder Blaise Matuidi is suspended and could be replaced by Clement Chantome, who could feature alongside David Beckham.
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