Two. Only Djokovic and Murray are a genuine force at the majors (at present, and even that is conditional), while Federer is struggling to win that final major as the door closes on his career. Nadal is not in any majors conversation anymore, and cannot be expected to win the 2017 French Open.
The rest of the more "notable" names in the field--
Thiem,
Isner,
Nishikori, Kyrgios, Dimitrov, Simon, and a boatload of other ATP failures are doing nothing, except collecting checks for aging.
Keep in mind that the ATP's "younger generation" are all aging and could not
steal a major if their lives depended on it. On the WTA side, Muguruza made her breakthrough by reaching the Wimbledon final in 2015, and followed that by winning a major in 2016. That is progression that does not exist among the
non "big two" ATP. And on that note, your:
..is a poor comparison, for two reasons:
- Muguruza--unlike a veteran such as Murray (yes, he is a veteran)--is a fresh player who broke through in fairly quick time, and is just getting started, but you're comparing her to a man who has been neck deep in his pro career for 11 years? By the way, that's 11 years and he only has 3 majors. Comparisons are not necessarily in Murray's favor.
- Murray is not yet an "all time great" player with only three majors. "All time great"--in theory--should be players who won a number not so common as three majors (which can be easily found throughout tennis history). It is great for a career, and he is forever a class above the innumerable players who never won a major, but there are levels of consideration to any list.