Não quero machucar o joelho de novo.

Quero is the 1st person singular form of the verb querer in the present tense.

• eu quero = I want
• você quer = you want
• ele/ela quer = he/she wants

In this sentence, the subject eu is omitted because Portuguese often leaves out subject pronouns when the verb form already makes the subject clear.

So:

• Não quero... = I don’t want...

It can say Eu não quero machucar o joelho de novo, and that would still be correct. But in Portuguese, subject pronouns are often dropped when they are obvious from the verb.

Since quero clearly means I want, eu is unnecessary unless you want emphasis or contrast.

For example:

• Não quero machucar o joelho de novo. = neutral
• Eu não quero machucar o joelho de novo. = slightly more emphatic, like I don’t want to hurt my knee again

In Portuguese, the normal way to make a sentence negative is to put não directly before the conjugated verb.

So:

• quero = I want
• não quero = I do not want / I don’t want

This is very standard word order in Portuguese.

Examples:

• Não sei. = I don’t know.
• Não posso ir. = I can’t go.
• Não quero machucar o joelho de novo. = I don’t want to hurt the knee again.

Because it follows quero.

After verbs like querer, Portuguese commonly uses an infinitive for the next action:

• quero comer = I want to eat
• quero dormir = I want to sleep
• quero machucar = I want to hurt

So the structure is:

• não quero + infinitive

In this sentence:

• não quero machucar = I don’t want to hurt

Machucar usually means to hurt, to injure, or to bruise, depending on context.

In everyday Brazilian Portuguese, it is very common and natural when talking about physical injury.

Examples:

• Machuquei o braço. = I hurt my arm.
• Não quero machucar o joelho. = I don’t want to hurt the knee.

Compared with other verbs:

• machucar is very common in everyday speech
• ferir also means to injure/wound, but it can sound more formal or more serious depending on context

So here, machucar is exactly the kind of verb a Brazilian speaker would naturally use.

This is a very common feature of Portuguese.

When talking about body parts, Portuguese often uses the definite article instead of a possessive adjective, especially when it is already obvious whose body part is meant.

So Portuguese often says:

• machuquei o braço = I hurt my arm
• lavei as mãos = I washed my hands
• quebrou a perna = he/she broke his/her leg

In English, we usually prefer my, your, his, etc. In Portuguese, the article is often enough.

So:

• o joelho literally = the knee
• but in natural English meaning here = my knee

Yes, joelho is masculine singular, which is why it uses o:

• o joelho = the knee
• os joelhos = the knees

There is not always a perfect rule for noun gender, so often you simply have to learn it with the article. A good habit is to memorize nouns as a unit:

• o joelho
• not just joelho

That makes it easier to remember gender correctly.

Here, de novo means again.

So:

• machucar o joelho de novo = to hurt the knee again

This is a very common everyday way to say again in Brazilian Portuguese.

Examples:

• Faz de novo. = Do it again.
• Ele caiu de novo. = He fell again.

You may also see novamente, which also means again, but de novo is usually more common and conversational in everyday speech.

Yes, but the difference is mostly about style and tone, not basic meaning.

• de novo = very common, conversational, natural in speech
• novamente = also correct, often a bit more formal or written

So these both work:

• Não quero machucar o joelho de novo.
• Não quero machucar o joelho novamente.

In everyday Brazilian Portuguese, de novo is probably the more natural choice.

Because it naturally modifies the action machucar o joelho.

Portuguese often places expressions like de novo after the main action:

• Quero ver de novo. = I want to see it again.
• Ela ligou de novo. = She called again.
• Não quero machucar o joelho de novo. = I don’t want to hurt my knee again.

Putting it at the end sounds very natural here.

A rough pronunciation guide is:

Nown KÉ-ro ma-shoo-KAR oo zho-EL-yoo djee NO-voo

A few important pronunciation notes:

• Não has a nasal sound. It does not sound like English now exactly.
• quero sounds roughly like KEH-ro, with the stress on the first syllable.
• machucar is stressed on the last syllable: ma-chu-CAR
• j in joelho sounds like the s in measure or the zh sound
• lh in joelho is a special Portuguese sound, somewhat like ly in million, though not exactly
• de before a word starting with n often sounds like djee in many Brazilian accents

You do not need to pronounce every word exactly like the spelling suggests in English; Portuguese sound patterns are quite different.

Yes, and that changes the focus a little.

• Não quero machucar o joelho de novo. = I don’t want to hurt my knee again.
• Não quero me machucar de novo. = I don’t want to hurt myself again.

The original sentence is specifically about the knee.
The version with me machucar is broader and means hurting yourself in general.

So if the knee is the important part, the original sentence is the better choice.