Create Expression from Func

You can not recreate an expression based on a method since an expression needs to know the original statements, not IL. You can however create an Expresson which makes a method call to your func like:

Func<int> func = () => 1;
Expression<Func<int>> expression = Expression.Lambda<Func<int>>(Expression.Call(func.Method));

Note however that systems like EF can't really work with this

While you could just create an expression tree which calls your delegate, it's unlikely to be useful - because the delegate will basically be a black box as far as the code analyzing the expression tree is concerned. Assuming you're trying to use something like LINQ to SQL, the query analyzer will need to be able to peer into your logic to convert it to SQL - and it can't do that if it reaches a plain delegate.

You should probably change the code which comes up with the delegate in the first place, to create an expression tree instead.