You may want to steer clear of John McEnroe today. Any minute now, CNBC is expected to pull the plug on the short-tempered tennis ace's struggling talk show. Ever since debuting last summer, McEnroe has caused nary a blip on Nielsen's radar. In fact, viewership was so low at times that it couldn't even be measured — a horror even WB's The Mountain hasn't suffered. The Big Deal with Donnie Deutsch is expected to take over the show's 10 pm time slot.