Strauss's side were beaten 2-0 from their three-match series against South Africa, which in turn saw the Proteas leapfrog them in the overall standings.
Reflecting on the defeat, Strauss has admitted that the South Africans were worthy victors.
"We're all bitterly disappointed. There was always going to be a lot to do. It was an outstanding Test match but South Africa played the better cricket and they've deserved it, although losing our number one ranking is a bitter pill to swallow," Strauss told BBC Sport.
Next up for England is a tour of India in November.