يحتاج صديقي إلى الراحة.

Yes. In Modern Standard Arabic, starting a sentence with the verb is very common, so يحتاج صديقي إلى الراحة is a perfectly natural word order.

You can also say صديقي يحتاج إلى الراحة. That version is also correct, but it gives a little more focus to my friend. Very roughly:

• يحتاج صديقي إلى الراحة = neutral statement
• صديقي يحتاج إلى الراحة = my friend needs rest

يحتاج is the 3rd person masculine singular imperfect form of the verb احتاج.

That means it matches صديقي because صديقي is singular and masculine.

So:

• احتاج = he needed / he came to need
• يحتاج = he needs / he is needing

If the subject were feminine, you would say:

• تحتاج صديقتي إلى الراحة = my female friend needs rest

Because in standard Arabic, احتاج / يحتاج normally takes the preposition إلى before the thing needed.

So the usual pattern is:

• يحتاج إلى + noun
• يحتاج إلى أن + verb

Examples:

• يحتاج إلى الراحة = he needs rest
• يحتاج إلى المال = he needs money
• يحتاج إلى أن يستريح = he needs to rest

This is different from English, where need can take a direct object without a preposition.

صديقي means my friend.

It is made of:

• صديق = friend
• ـي = my

So the ـي is a possessive suffix meaning my. Arabic often attaches possessive pronouns directly to the noun instead of using a separate word.

Compare:

• صديق = a friend / friend
• صديقي = my friend
• صديقك = your friend
• صديقه = his friend

In Arabic, abstract nouns are often used with الـ even when English uses a bare noun with no article.

So الراحة here is the natural way to say rest in a general sense.

This does not have to be translated as the rest in English. In many cases, the Arabic definite article is simply part of the normal idiomatic expression.

So:

• يحتاج إلى الراحة = he needs rest

Using راحة without الـ is possible in some contexts, but in this sentence الراحة is the most natural standard choice.

It is in the genitive case because it comes after the preposition إلى.

In fully vocalized Arabic, the sentence is:

يَحْتَاجُ صَدِيقِي إِلَى الرَّاحَةِ

The final -i sound on الرَّاحَةِ marks the genitive.

So:

• after إلى, the following noun is genitive
• الرَّاحَةِ = genitive form of الرَّاحَة

Because ر is a sun letter, the ل of الـ is not pronounced separately. Instead, it assimilates to the ر.

So الراحة is pronounced:

• ar-rāḥa in pause
• ar-rāḥati in full formal pronunciation with case ending

Not:

• al-rāḥa

Also, the final ة is usually heard as:

• -a / -ah when pausing
• -t in full grammatical pronunciation before the case ending, as in الرَّاحَةِ

Not always. The Arabic imperfect can express present or future, depending on context.

In this sentence, the most natural meaning is present: he needs.

If you want to make the future clearer, you can use:

• سيحتاج صديقي إلى الراحة = my friend will need rest
• سوف يحتاج صديقي إلى الراحة = my friend will need rest

So the bare يحتاج is often understood from context.

Yes. A very common alternative is:

يحتاج صديقي إلى أن يستريح

This means my friend needs to rest.

So Arabic gives you two natural options:

• يحتاج صديقي إلى الراحة = my friend needs rest
• يحتاج صديقي إلى أن يستريح = my friend needs to rest

The first uses a noun (rest), and the second uses a verb (to rest).

The dictionary form is احتاج.

So if you look it up, you would usually find:

• احتاجَ = to need

Its present/imperfect form is:

• يحتاجُ = he needs

This verb is related to the idea of need, which you also see in the noun حاجة meaning need.