Marc-Andre ter Stegen was not present in Barcelona training on Monday and faces a race against time to prove his fitness ahead of Tuesday's Champions League clash with Porto.
The goalkeeper withdrew from the Germany squad for this month's international break as he battled a back injury which also forced him to miss the weekend's 1-1 draw with Rayo Vallecano.
Ter Stegen had hoped to return to action quickly, confirming on social media that he was "coming back soon", but it appears that comeback may not be imminent as manager Xavi revealed the goalkeeper is yet to return to training.
"Tomorrow, Marc will have a fitness test," Xavi told the media. "We'll see how he is.
"He hasn't trained, so tomorrow he will test to see if he is 100%."
In Ter Stegen's place, Inaki Pena started against Vallecano and would likely retain his spot in the starting lineup against Porto.
Barcelona head into the game on an underwhelming run of form which included a 1-0 defeat to Shakhtar Donetsk last time out in Europe.
Xavi's side are top of Group H but tied on both points and goal difference with Tuesday's opponents, with the winner of the upcoming affair set to take a huge step towards qualification for the knockout stages.
A defeat would likely end Barcelona's hopes of topping the group but would also open the door to Shakhtar, who are just three points behind and will expect to close that gap when they face Royal Antwerp earlier in the day, to snatch the final qualification point.
The Ukrainian side do, however, have a significantly poorer goal difference and would require a seven-goal swing to overtake Barcelona this round.
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This article was originally published on 90min as Barcelona star misses training ahead of crunch Champions League clash with Porto.