[Anton]

I've had two lettuces (red variety) shrivel up on me (a couple of leaves turn odd before the whole plant perishes) despite supplying water everyday in this heat. They were transplanted from pots I should add. Could this be a fungal disease and if so is there any prevention or cure? And do I dare put another lettuce plant in its place?

Anton

[WG.]

Sounds like cutworm.  Was the stem chewed through?

[Anton]

I didn't look at the stem. I just notice the leave were starting to look grungy, perishing. and if it is cutworm?

Anton

[Oscar Too]

could be botrytis - kind of grey mould and rot?

You may have planted them too close together, especially if you are watering every day.  They need ventilation to keep them healthy, especially frizzy types - lolla bionda and so on.  12 inches apart should do it.

[WG.]

I didn't look at the stem. I just notice the leave were starting to look grungy, perishing. and if it is cutworm?

Anton

I would replant regardless.  You will find that losses are inevitable amongst lettuce (in fact among nearly all crops).  Doubtless a bug of some kind since viral diseases aren't common. Reckon your new plants will have the same chance as the others.