Barca host their bitter city rivals on Sunday sitting two points behind leaders Real Madrid, who are at home to Celta Vigo on Saturday, before welcoming PSG on Wednesday for a match that will decide who finishes in first place in Group F.
With five of six matches played, PSG lead on 13 points thanks to their 3-2 win over Barca in Paris in September, with the Catalan club on 12 in second.
Both sides are through to the last 16, where they will be anxious to avoid being paired with a group winner.
"All the matches are important but it's true that we are really up for games like these," Bartra told a post-training news conference.
"They are tests that if we win them will make us stronger," added the Spain international. "We have to win, above all try to play well, and the team is in good shape going into these two games."
Bartra, who played at Espanyol when he was a boy before joining Barca's academy, defended new signing Douglas, a fullback who joined from Sao Paulo in his native Brazil in the close season.
Douglas has only featured twice for Barca this term and his performance against Huesca in the King's Cup on Wednesday prompted widespread criticism and even ridicule in local media.
The 24-year-old, who typically plays at right back, was compared with some of Barca's recent signings who have failed to live up to expectations including midfielders Alex Song and Aleksandr Hleb and defender Dmytro Chygrynskiy.
"It's very hard arriving from another continent and adapting to a European team," Bartra said.
"Imagine what it must be like to adapt to Barcelona, and he didn't even speak the language.
"Douglas is trying to improve and adapt in every training session and the important thing is he continues with that, working hard and performing well when he plays."
(Writing by Iain Rogers, editing by Toby Davis)
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