Can growth hormone deficiency affect testosterone levels?

Not usually: Although both testosterone and growth hormone are stimulated by hormones from the pituitary gland, they are relatively unrelated.

To some extent: Decline in hgh can lower the production of several other hormones to some extent. Aging is accompaned by declining testosterone levels also. Referred to as andropause. The decline is not as swift and dramatic as womens menopause, but it does cause symptoms that are reversed with testostterone replacement.

Likely: There are gh receptors, igf-1 and gh releasing hormone receptors on the leydig cells. Boys born gh deficient have micro penis often. Their testes don't respond normally to lh during gestation. Pubertal development is hampered by gh deficiency until replaced. Men with gh deficiency can have impaired fertility. Replacing gh increases seminal fluid. Not sure if testo levels change +/- gh in adults.