His work lasts until Fajr; can he put Zuhr and ‘Asr together?

Praise be to Allah.

Firstly:

What is required of those who have jobs and others is to offer the prayers on time, because Allah, may He be exalted, says (interpretation of the meaning): {Prayer is prescribed for the believers at specific times} [an-Nisa’ 4:103]. Allah, may He be exalted, praises the believers for not being distracted by their work from obedience to Allah, may He be exalted, as He says (interpretation of the meaning):

{[Are] men whom neither commerce nor sale distracts from the remembrance of Allah and performance of prayer and giving of zakah. They fear a Day in which the hearts and eyes will [fearfully] turn about,

That Allah may reward them [according to] the best of what they did and increase them from His bounty. And Allah gives provision to whom He wills without account} [an-Nur 24:37-38].

So what you must do is strive to wake up at the time of prayer, and take measures that will help you to do that. Then if it so happens that sometimes you sleep and miss praying in congregation, even though you are keen to wake up and took means to help you to do that, there will be no blame on you.

Secondly:

If someone travels to a city and intends to stay there for more than four days, then he comes under the same ruling as a resident; he must offer the prayers in full and it is not permissible for him to put two prayers together because of travelling. But putting prayers together is not something that is only for travelling; rather it is permissible for other reasons, such as sickness, rain and hardship.

This has been discussed previously in the answer to question no. 38079 .

Based on that, if you think it is likely that you will not be able to wake up to pray Zuhr, and that is too difficult for you, there is nothing wrong – if Allah wills – with delaying Zuhr so that you can put it together with ‘Asr at the time of the later prayer, provided that you only do that when it is too difficult for you, and it does not become something that you do all the time, regardless of whether you experience hardship or not.

And Allah knows best.