Short answer. Only in an emergency. Under Article 1802, where the partners stipulated that no managing partner may act without the others' consent, the concurrence of all is necessary for an act to be valid — and the absence or disability of one cannot be used as an excuse, unless there is imminent danger of grave or irreparable injury to the partnership.
What the law says
the concurrence of all shall be necessary for the validity of the acts
Civil Code, Article 1802 — Unanimity-Required Management. Read the full provision →
Unanimity is the rule they chose
Article 1802 applies when the partners have deliberately tied their managers together. If they stipulated that none of the managing partners shall act without the consent of the others, then the concurrence of all shall be necessary for the validity of the acts. This is stricter than the default for multiple managers, and it is a choice: the partners have decided that important management should be a joint act, requiring everyone's agreement, rather than something any one of them can do alone.
No excuses for a missing manager
The article anticipates a common workaround and blocks it. Where unanimity is required, the absence or disability of any one of them cannot be alleged as a reason to proceed without him. So a manager who is away, ill, unreachable or otherwise unable to take part is not simply written out of the decision; his consent is still needed, and the others cannot act in his stead by pointing to his unavailability. This can be inconvenient, but it is the direct result of the partners' own stipulation. Having insisted that nothing be done without everyone, they cannot then treat one manager's absence as licence for the rest to act — the requirement holds even when it is awkward.
The one exception: imminent grave injury
There is a single, narrow escape. The unanimity requirement, and the bar on excusing a missing manager, both give way unless there is imminent danger of grave or irreparable injury to the partnership. In a genuine emergency — where waiting for everyone's consent would expose the firm to serious, imminent harm that could not be undone — a manager may act to protect the partnership even without the others' concurrence. But note how tightly this is drawn: the danger must be imminent, and the threatened injury grave or irreparable.
Practical takeaways
If your agreement requires all managers to consent, run the firm accordingly: get everyone's agreement on management acts, and do not assume one manager can act simply because another is away. Build a workable way to obtain consent — even remotely — so ordinary business is not paralysed by the rule you chose. Reserve solo action for true emergencies that fit the imminent-grave-injury exception, and document why the situation qualified. And if the unanimity rule is proving unworkable for everyday matters, the answer is to amend the agreement, not to ignore a requirement that makes non-conforming acts invalid.