Off to Freiburg in July for a week with work and have one day free for some MTB riding, but struggling to find a local bike shop to hire a bike, any recommendations?

Not too sure about Freiburg itself but in the wider Black Forest area, it is worth giving the tourist office a shout. I suspect that the bikes may be a little more “German touring MTB” rather than somethinf a little more capable.

Feldberg is about an hour away and is the biggest “mountain” in the area –

https://www.blackforest-tourism.com/Media/Attraktionen/Bike-rental-Feldberg

also there is a little bike shop in Bonndorf, not sure they rent but the owner, Peter is very knowledgeable and speaks perfect English if your German isn’t passable. I have a feeling he does group rides around the black forest too (inc some techy stuff).
https://www.via-velo.de/

There’s a bikepark in Todnau that hires enduro/dh bikes, if that’s the kind of thing you’re after?
The owner is American so you’d have no problem with communication.

If you get the chance, take the Schauinsland lift and follow the “enduro” trail down into Canadian Trail – it’s a brilliant way to spend a couple of hours.
Baden to the Bone is also excellent, but the climb back out is a killer!

Have fun. Freiburg’s a bloody awesome place.

Another option would be to get the train a short distance away to Kirchzarten where they run a bike marathon race every year. Lots of marked trails. We stayed in Kirchzarten for a week on holiday a couple of years ago. There is definitely enough riding there to tempt me back.

There are at least a couple of bike shops. You’d need to check if they do rentals, I expect they should do! http://www.sport-eckmann.de is one, I think the other is called Velo.

Freiburg is a great little town.

Lots of bike shops.

Google bike shop Freiburg and give a few shops a bell. I’m sure one or more will have a bike spare for you to ride for the day.

Todtnau/Tittisee are a bit of a drive and the trails in Freiburg are top quality. Stay in Freiburg.

Love Freiburg.Have fun