יש חשש רציני.

יש is the Hebrew existential word meaning there is / there are.

So יש חשש רציני literally means something like:

• there is a serious concern
• there exists a serious concern

It does not mean has by itself. In other contexts, יש לי means I have, but that is literally there is to me.

Hebrew does not have an indefinite article like English a / an.

So חשש רציני can mean:

• a serious concern
• serious concern (depending on context)

If the noun were definite, Hebrew would use ה־:

• החשש הרציני = the serious concern

In this sentence, the noun is indefinite, so there is no ה־.

In Hebrew, adjectives normally come after the noun they describe.

So:

• חשש רציני = a serious concern
• literally: concern serious

This is the normal word order in Hebrew.

רציני is the masculine singular form of the adjective serious.

It matches חשש, which is also masculine singular.

Some other agreement forms would be:

• masculine singular: רציני
• feminine singular: רצינית
• masculine plural: רציניים
• feminine plural: רציניות

So if the noun changed, the adjective would change too.

חשש is masculine.

That is why the adjective is רציני and not רצינית.

A good way to remember this is that adjectives in Hebrew must agree with the noun in:

• gender
• number
• definiteness

Here:

• חשש = masculine singular, indefinite
• רציני = masculine singular, indefinite

חשש is a noun meaning concern, fear, apprehension, or suspicion, depending on context.

In this sentence, it usually has the sense of:

• concern
• serious worry
• real apprehension

It is somewhat more formal or neutral than a word like פחד, which is more like fear.

So יש חשש רציני sounds like:

• there is real cause for concern
• there is serious concern

Not in the same way English does.

Hebrew usually does not use a present-tense copula equivalent to is / am / are in simple sentences like:

• הוא עייף = he is tired
• הבית גדול = the house is big

But here, יש is not exactly the ordinary verb to be. It is an existential form meaning there is / there are.

So this sentence is built as:

• יש = there is
• חשש רציני = a serious concern

That would mean something slightly different.

• יש חשש רציני = there is a serious concern
• החשש רציני = the concern is serious

The sentence you gave introduces the existence of a concern.
The second version talks about a specific concern that is already known.

So יש is used because the sentence is presenting something as existing.

In normal speech, יש חשש רציני is the natural order.

Hebrew usually keeps this pattern with יש:

• יש + noun phrase

So:

• יש חשש רציני = natural
• יש רציני חשש = incorrect / unnatural

You may sometimes see unusual word order in poetry or very marked speech, but for everyday Hebrew, stick with יש חשש רציני.

The negative of יש is אין.

So:

• יש חשש רציני = there is a serious concern
• אין חשש רציני = there is no serious concern

This is a very common pattern in Hebrew:

• יש זמן = there is time
• אין זמן = there is no time

In the past and future, Hebrew does not use יש in the same way.

You would usually say:

• היה חשש רציני = there was a serious concern
• יהיה חשש רציני = there will be a serious concern

So:

• present: יש חשש רציני
• past: היה חשש רציני
• future: יהיה חשש רציני

חשש is pronounced approximately kha-SHASH.

Things English speakers often notice:

• The letter ח is not like English h. It is a throatier sound, like the ch in German Bach or Scottish loch.
• The stress is on the last syllable: kha-SHASH.
• ש here is sh.

So the whole sentence is roughly:

yesh kha-SHASH re-tzi-NI

with the main stresses on:

• חשש
• רציני

It is fairly neutral and can sound a bit formal, depending on context.

It would fit well in:

• news reports
• official statements
• medical or legal contexts
• serious everyday conversation

For example, it could mean:

• there is serious concern about the situation
• there is a serious risk / worry

So it is a very natural sentence, especially in more serious contexts.