Waiting for McKinsey offer letter

Hi,

I am super excited that I received an Associate offer from McKinsey (European office) last Wednesday. I was congratulated by the HR Head and informed that he is preparing my offer letter and visa plan and will share the same shortly.

However, it has been a week now and I am yet to receive the formal offer letter. I guess there may be some visa technicalities since I need to be sponsored, but does that have a bearing on the time to send across the formal offer letter? Would much apprecicate any inputs.

PS: I connected with the HR's assistant today and she congratulated me too, but the HR Head is yet to officially share an update since he offered me the role last week (after a total of 7 interviews).