Davalac krvi je u nevolji.

Literally, davalac krvi means giver of blood, which is the usual Serbian way to say blood donor.

• davalac = giver / donor
• krvi = of blood

The noun davalac is formed from the verb davati (to give) plus a noun-forming ending that creates a person who does the action.

So structurally, Serbian uses [person] + [of what], where English often uses a compound like blood donor.

Because Serbian uses the genitive case here.

The basic form is:

• krv = blood

But after a noun like davalac, Serbian normally puts the second noun into the genitive to mean of blood:

• davalac krvi = donor of blood

This is a very common pattern in Serbian:

• čaša vode = a glass of water
• karta grada = a map of the city
• davalac krvi = blood donor

So krvi is the genitive singular form of krv.

Je is the 3rd person singular present of the verb biti (to be).

So:

• je = is

In this sentence, it links the subject and the rest of the statement:

• Davalac krvi je u nevolji.
• The blood donor is in trouble.

Unlike in some Slavic languages, Serbian normally does use the present-tense form of to be in sentences like this.

Nevolji is in the locative singular.

That is because the preposition u can mean in, and when it expresses location or a state, it usually takes the locative:

• u nevolji = in trouble
• literally: in difficulty/distress

The basic noun is:

• nevolja = trouble, difficulty, distress

Its locative singular is:

• nevolji

So:

• u + locative → u nevolji

Because u can take different cases depending on the meaning.

• u + locative = being in a place/state
• u + accusative = movement into a place/state

Here, the sentence describes a condition or situation, not movement:

• Davalac krvi je u nevolji. = the donor is in trouble

So Serbian uses the locative: u nevolji.

If you used u nevolju, it would suggest motion into trouble, which is a different idea.

Yes, very much so.

Biti u nevolji is a common Serbian expression meaning:

• to be in trouble
• to be in difficulty
• to be in distress
• sometimes to be in need

So even though nevolja literally means something like trouble / hardship / misfortune, the whole phrase u nevolji works as a natural idiomatic expression.

Serbian has no articles like English a/an/the.

So davalac krvi by itself can mean either:

• a blood donor
• the blood donor

The exact meaning depends on context.

That means the sentence could be understood as either:

• A blood donor is in trouble
• The blood donor is in trouble

In real use, surrounding context tells you which one is meant.

No, Serbian word order is fairly flexible, although this version is the most neutral and straightforward.

This order:

• Davalac krvi je u nevolji.

is the natural subject + verb + phrase order.

But other orders are possible for emphasis, for example:

• U nevolji je davalac krvi.

This might sound more marked, as if you are emphasizing in trouble.

Because Serbian marks relationships through case endings, word order can move around more than in English. Still, the sentence you were given is the best neutral pattern for a learner to copy.

Yes, donor krvi is understandable and used, especially in modern or medical-style language.

However, davalac krvi is a very standard and native Serbian expression.

So:

• davalac krvi = very normal, standard Serbian
• donor krvi = also possible, but less purely native in feel

If you are learning standard everyday Serbian, davalac krvi is an excellent phrase to know.

Davalac is a masculine noun in the singular nominative.

In this sentence, it is the subject, so it appears in its basic dictionary form:

• davalac

You will often see masculine nouns like this as subjects in the nominative.

Its form may change in other cases, but here it stays in the base form because it is the one doing or being described in the sentence.

You replace je with nije:

• Davalac krvi nije u nevolji.
• The blood donor is not in trouble.

This is the normal negative form of is in Serbian:

• je = is
• nije = is not

So the rest of the sentence stays the same.