Sounds like the starter is beginning to fail, since you say you hear a single click... My '94 had a stubborn NSS, so I had to bump the shifter forward before I tried starting it, but you wouldn't or shouldn't get any click if that was the issue... Smacking the starter with a hammer, as suggested, may do the trick, for now...
'72 CJ5 Ren
'91 XJ, '96 XJ, '98 XJ
'94 ZJ, '96 Orvis ZJ
'98 Platinum 5.9, '98 Slate 5.9 (DD)