No speaker, with the exception of very simple single driver systems, will remain close to its rated "nomimal" impedance throughout its frequency range. That means the actual load the amplifier must work into varies with frequency. As a rule, if a manufacturer rates their speakers at four Ohms, the actual impedance of the load is, within some frequency band, safely assumed to be lower by a good margin than what the "nominal" (average) rating implies. If that low impedance point falls in the lower octaves, then the problem is worsened by the fact most low frequency signals require the most power applied. Should the low impedance point exist at higher frequencies, a rare but not unrealistic propostion, then the amplifier needs only to manage a few watts by comparison and the load is deemed not as "difficult". It would therefore benefit you to know more about the speaker's actual load characteristics than just the notion it is a "four Ohm" system. The speaker manufacturer should be able to provide the information you would need to determine just how difficult any speaker is for most amplifiers.
To be safe you would want to consider any four Ohm rated speaker to be a very difficult load for most amplifiers in the budget category. Compounding the issues of impedance you must also include the electrical phase angle of the load which in most four Ohm rated systems would also tend towards being a difficult load. Given the assumed difficulty of the actual load an amplifier must produce large amounts of amperage (current) on demand. This is exactly where budget priced amplifiers fail, they are not built to produce current and their wattage ratings are not realistic into reasonable real world loads. In other words their test bench spec'd wattage is not actually available when driving real world speakers playing actual music material and not just a test tone with the receiver hooked to a load resistor. Buying more wattage is not an answer since the need is for current which is only one component of "watts". High wattage on a test bench does not always translate into high current in use. There are receiver companies that advertise their products as "high current" and they would give you the best chance at surviving a low impedance load.
If your volume requirements are minimal, lets say background levels to conversational levels and nothing above that, and you provide maximum ventilation (air flow) to the amplifier you might get by with most less expensive receivers surviving a "nominal" four Ohm load. Above those levels and most receivers of any stripe or cost will overheat and eventually shut down. Receivers with load switches such as "8-6 Ohms" will reduce the available current which will somewhat reduce sound quality during those demanding pasages of music but might possibly keep the receiver from self destruction. The other work around would be to play very simple music which does not challenge the power supply of the receiver.
If none of those conditions fit your situation, then you should either buy a more capable amplifier or not buy "four Ohm" speakers.