Involved in the biosynthesis of the dTDP-L-rhamnose which is a component of the critical linker, D-N-acetylglucosamine-L-rhamnose disaccharide, which connects the galactan region of arabinogalactan to peptidoglycan via a phosphodiester linkage (PubMed:12029057). Catalyzes the reduction of dTDP-6-deoxy-L-lyxo-4-hexulose to yield dTDP-L-rhamnose (By similarity). dTDP-beta-L-rhamnose + NADP(+) = dTDP-4-dehydro-beta-L-rhamnose + H(+) + NADPH Binds 1 Mg(2+) ion per monomer. Carbohydrate biosynthesis; dTDP-L-rhamnose biosynthesis. Was identified as a high-confidence drug target. Belongs to the dTDP-4-dehydrorhamnose reductase family.