@Aaftab Mughal; Also bear in mind that If the Passat wheel has a 235/45 R17 tyre and the tyres on your Leon are 225/45 R17, then Passat tyre will have a slightly higher sidewall, which will mean the radius and overall circumference of the Passat wheel/tyre will be larger than that of your existing wheels/tyres;
Your tyres (225/45 R17) - sidewall height = 225 x 45% = 101.25 mm
Passat tyre (235/45 R17) - sidewall height = 235 x 45% = 105.75 mm
Tyre sidewall height difference; 105.75 - 101.25 = 4.5mm, so the Passat wheel will be rotating at a slightly different speed to the other three wheels.
Bear in mind that by fitting one odd sized tyre, if the tread depth and tread pattern is different to the other wheel / tyre on that same axle, then your car may handle unpredictability in the event of having to make an emergency manoeuvre (hard braking or swerving manoeuvre). I don’t know if there are any legal issues if one tyre on the car is a different size to the remaining three, but it might be worth checking this out.
In your position, I’d only use an odd wheel / tyre in the same way as a temporary space saver spare - i.e. only put it on the car to get me to a tyre fitting place to get your flat tyre repaired or replaced.