The Italian midfielder missed the Magpies’ 1-0 win at Chelsea in the Premier League on Saturday evening due to illness but has travelled to the Camp Nou.
United are looking to progress into the last eight of the Champions League for the first time in their history with the tie level at 1-1 from the first leg at St James’ Park.
Tonali trained with his teammates last night and it is hoped he will be in a position to take his place back in midfield.
"We'll have a look at it today,” Howe said. “Today's the first day we've seen him. (It's) an opportunity for hopefully him to train, if he feels strong enough. We'll make a decision tomorrow."
Joe Willock has also been passed fit after he withdrew in the latter stages at Stamford Bridge. Bruno Guimaraes remains sidelined until after the international break but is in Barcelona to support his teammates,
Here are our Newcastle United are predicted to line-up:
1. GK: Aaron Ramsdale
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2. RB: Kieran Trippier (in for Tino Livramento)
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3. CB: Malick Thiaw
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4. CB: Dan Burn (in for Sven Botman)
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