Either you damaged roots or some roots were exposed to air for to long. It is a coin toss as to if it will recover or not. It might be fine and it might die. It was mentioned that SuperThrive might not be a bad idea. It does help to reduce plant shock.
 
Ok, there is one other possibility depending on how you transplanted. If you did not give the plants a real good soaking after transplanting it is possible the soil around that one plant’s roots is just to loose. That is a low probability chance but it is still a chance.
Since it is obviously outside it would be a good idea to block the wind to the plant as much as possible and maybe even cut back slightly on the light for a few days .. like if there is a slightly shady place you can put the plant and protect it from wind … that would be the place to put it now.  
Something else you can do is to trim back your plant, cut it back to a size that the root system can support. Not knowing what damage was done or to what extend it is hard to know how much to cut but if your options are to lose a plant or cut maybe one third of it back so it lives ….. which route will you take?
 
It’s a tough call …… sit it out and see if it comes around and risk losing it or take action that in the end might not have been needed to take?
For future reference .. when you repot follow the following steps.
 
Select the pot size you will be transplanting into. (I suggest growing in nothing smaller than 5-gallon pots and I normally use 7-gallon pots and I start out my plants in them and never repot.)
 
Allow the soil in the pot your plant is in to dry out and slightly pull away from the sides of the pot.
 
(The following applies if you are right handed. If not reverse the hand position/use instructions)
 
Partially fill your new larger pot with quality soil so when you insert your plant into the new pot and fill in around the rootball the top of the soil will be at the correct level.
 
Pick up your old pot with your left hand.
 
Place your right hand on top of the soil with the main stem between your first and second fingers.
 
Gently tap the edge of the pot on a countertop or a workbench or something similar. The entire rootball should slide out in one piece, possibly with a slight amount of soil loss, but no damage to or loss of roots unless the plant was so root-bound that the roots had grown through the drain holes. If that is the case clip them first.
 
Your plant and rootball are then securely held in your right hand. Inspect the rootball and if it is tightly packed/twisted/root-bound slightly score/cut the edges of the rootball and also slightly score/cut the bottom of the rootball.
If you do not score/cut the root-ball that the roots will want to continue to follow their circling pattern and their growth progression both down and to the sides into the fresh deeper soil will be much slower. Each cut root will push out new roots and they will go both out and down into the new soil.
 
Place the plant into the new pot.
 
If the surface level of the old rootball is to low or two high remove some soil or add additional soil.
 
Next fill in around the edges between the rootball and the sides of the larger pot.
 
Water thoroughly to cause the soil to settle without compressing it too much by packing it down by hand. If needed add additional soil and water again.
 
Normally plants will undergo very little to no shock when transplanted in this manner but it would not be an injudicious thing to do to use a product like SuperThrive or something with the same general properties because they will reduce plant stress helping them to overcome it quicker and easier.
You can still use SuperThrive but I am not sure if it will be a case of closing the barn door after the horse has gotten out but it is worth a try and it is not a bad thing to have and use anyway so I say give it a try.
Whoa .... slow down ....... looks like it is dry ........
set it in the shade for a while and give it a good watering make sure you have good drainage ....... don't try and do too much all at once .........
I've transplanted many plants ... I let em dry a little before transplant and water well after transplant ...........
looks to me like they need a drink
spraying with plain water (chemical free water) may help ....... but the roots need water .... u might have some other probs ... since u said this is the only one so far ........... but I'd start with water
plants below were intentionally dried before transplant ... 2nd pic is about 9 weeks later
As long as you know she has enough water, leave her be and she should be fine. This happened to one of my plants - not only did I rip off a good portion of her tiny roots while transplanting, but I also FIMmed her right before, too. It took her about five days or so to come out of it.
liquid karma, superthrive, hydroguard, compost teas, B1, all these things help. B1 really helped but I would take superthrive over that shit I think. Superthrive is really the shit. Also compost teas get your soil alive and the platns love that noticably.
I just transplanted my girl from a 5gal to 8gal while she is in veg. I fucked up and tore out ar 3/4 of her roots. She looked alright a day later, but come today (2days later) she looks really sad. She is extremely droopy, and is beginning to look defficients (brown spot on lower mature leaves). Is she going to die, or is there a way to save her? Please help
I have a plant that i just transplanted that looks just like that one but my plant is much smaller maybe 8" tall and I transplanted it into new compost that wa sugessted from just regular soil from my backyard. the first time i transplanted it I had no shock at all. I didn't lose a day of growth. now it seems to be helpless. All though it seems to have new growth in the very top of the plant but the leaves are sagging just like the picture in the above plant. it has been about 4 days and right after transplant it started to sag. and it has gone from looking good to looking sad but during sunlight times it looked worse than last night when it was in the cool night air it started to stiffen up and look as if it was coming back but the sun looked like it was making it worse. please if anyone can help ? I am on my way to get super thrive as a last resort.