Hence when attiny is in deep sleep mode, nrf24l01 is also switched off. This should considerably reduce the power consumption.
Theoretically speaking, Attiny's analog output pin can output around 40mA and nrf24l01's power consumption is 11.3mA transmitting, 13.5 receiving.
Thank you for your comments.
I'd tend to use a P channel mosfet to switch the NRF24L01 module because you have also got to consider the capacitors on the module power rails and any additional ones you may need to add during any troubleshooting.
Here is a schematic: NRF24L01 Test with Arduino - Wiki
Result: it works fine. nrf24 sends data to a separate receiver (nrf24+esp8266) Problem: after Attiny85 wakes up from deep sleep, nrf24 not sending data. I think this is more a programing issue. I will investigate it and revert.
Trial 2): powered nRF24 using P channel mosfet as suggested by 6v6gt (see attached picture)