The first thing that happens is the pituitary gland goes to sleep when it sees exogenous androgens. As the pituitary is the boss of the testes, and it stops telling them to make testosterone, blood levels drop. One dose at 250mg isn't enough to replace the amount of testosterone made by the testes, and after six days only about 60% of that shot is remaining. This is why it should be pinned twice a week for smaller doses, or the full dose (assuming 500mg/wk) every 7 days or so.
Check again in 4 weeks as vision suggests to get an accurate picture. FYI: 48 hours after an injection is the peak value seen in the blood stream, and the day of the next pin (before taking it) would be the trough.
I hope your "friend" isn't only cycling 250mg/wk, as that's barely over a replacement dose for most, and a complete waste of time and money.