Avoir le couteau sous la gorge is a French idiom that literally to “to have a knife under the throat” and means “to be under the gun”.
Avoir le couteau sous la gorge
to be under the gun

Example sentence
For the example sentence, I used the translation “to be under a lot of pressure”. Interestingly, the verb subvenir means to support, provide for or “meet the needs of”. The verb supporter means “to put up with” or “to tolerate”.
Pierre a certainement le couteau sous le gorge en ce moment. Il doit avoir assez d’argent pour subvenir aux besoins de sa famille et payer ses dettes.
Pierre is definitely under pressure now. He needs to have enough money to support his family and pay his debts.