Lekarsko uverenje će potvrditi zdravstvenu sposobnost.

Because lekarsko has to agree with uverenje, which is a neuter singular noun.

The adjective lekarski is the dictionary form (masculine singular). Its basic singular forms are:

• lekarski — masculine
• lekarska — feminine
• lekarsko — neuter

Since uverenje is neuter, the adjective becomes lekarsko.

It is nominative singular, because it is the subject of the sentence — the thing that will do the confirming.

So in Lekarsko uverenje će potvrditi zdravstvenu sposobnost, the subject is lekarsko uverenje.

A useful detail: uverenje is a neuter noun, and nouns of this type often end in -e.

This is the future tense in Serbian, often called Future I.

It is formed with:

• a form of hteti (ću, ćeš, će, ćemo, ćete, će)
• plus the infinitive

Here:

• će = will for he/she/it
• potvrditi = to confirm

So će potvrditi means will confirm.

Because the subject is lekarsko uverenje (it), the sentence uses će.

Because after će, Serbian normally uses the infinitive, not a present-tense form.

So:

• će potvrditi = will confirm
• potvrđuje = confirms / is confirming

Also, potvrditi is a perfective verb. That means it presents the action as a single completed event. That fits well here: the certificate will confirm something once, as a completed act.

If you used potvrđivati, that would sound more like repeated or ongoing confirming, which does not fit this sentence as naturally.

Because this phrase is the direct object of the verb, so it is in the accusative case.

The noun sposobnost is feminine singular, so the adjective must also be feminine singular accusative:

• zdravstvena sposobnost = nominative
• zdravstvenu sposobnost = accusative

So the form zdravstvenu shows that this phrase is the thing being confirmed.

Because many feminine Serbian nouns ending in a consonant have the same form in nominative singular and accusative singular.

So:

• nominative: sposobnost
• accusative: sposobnost

The case is shown more clearly by the adjective:

• zdravstvena sposobnost = nominative
• zdravstvenu sposobnost = accusative

This is very common with nouns such as mogućnost, odgovornost, sposobnost, and similar abstract nouns.

No, Serbian word order is fairly flexible, but there are rules about clitics like će.

The sentence as given is neutral and natural:

• Lekarsko uverenje će potvrditi zdravstvenu sposobnost.

You could also change the order for emphasis, for example:

• Zdravstvenu sposobnost će potvrditi lekarsko uverenje.

That shifts focus toward zdravstvenu sposobnost.

One important rule: će is a clitic, so it normally appears in second position in the sentence or clause.

Yes, in colloquial spoken Serbian, you may hear će da + present tense, for example:

• će da potvrdi

But in a formal or standard written sentence like this one, će potvrditi is the better choice.

So:

• će potvrditi — standard, especially in writing
• će da potvrdi — common in speech, more colloquial

Because Serbian does not have articles like English a/an/the.

So lekarsko uverenje can mean:

• a medical certificate
• the medical certificate

The exact meaning depends on the context.

The same is true for zdravstvenu sposobnost: context tells you whether English should use the, no article, or occasionally a, depending on the translation.

Yes, it is a very common phrase meaning a medical certificate or doctor’s certificate.

Grammatically, it is simply:

• lekarsko = medical / doctor’s
• uverenje = certificate / attestation

But together they function as a standard expression.

A learner may also see similar phrases such as:

• lekarski pregled = medical examination
• lekarska potvrda = doctor’s note / medical confirmation

So this sentence uses very normal formal vocabulary.