Using http_proxy in HAProxy 1.6.3 (no replies)

I have configured a backend as follows:

backend be-testing
mode http
option httpclose
option http_proxy

and hit this using Google's IP as:
wget --header="Host: http://216.58.197.46:80&quot; <vip>

but this fails with 503 error, debug shows:
00000003:fp-testing.clireq[0009:ffffffff]: GET / HTTP/1.1
00000003:fp-testing.clihdr[0009:ffffffff]: User-Agent: Wget/1.16 (linux-gnu)
00000003:fp-testing.clihdr[0009:ffffffff]: Accept: */*
00000003:fp-testing.clihdr[0009:ffffffff]: Host: http://216.58.197.46:80
00000003:fp-testing.clihdr[0009:ffffffff]: Connection: Keep-Alive

What am I doing wrong? Is it also possible to use DNS name with a newer
version of HAProxy?

Thanks,
- Krishna