A sure sign that a sitcom is fading is the continual presence of unusual guest stars with little or nothing to do with the original premise of the series. “Will & Grace” (7:30 p.m., NBC) limps into its seventh season with an exceptionally weak episode starring Jennifer Lopez as herself. For those who still follow the show, Jack insinuated himself into the pop star’s inner circle at the end of last season, and now they are inseparable. It’s about as funny as it is plausible.

Karen resents the time Jack spends with Jenny from the Block, and she tries to sell the singer a song that she and an unseen Rosario cooked up. Again, more contrived than funny. Deprived of funny lines, a bitter Grace reads the riot act to her cheating husband, Leo (the comically challenged Harry Connick Jr.). Enough already.

“Will & Grace” has survived any number of slumps, including the discovery of Jack’s son and the prolonged story about Grace possibly carrying Will’s baby. So maybe viewers will forgive a season opener this flat and unfunny. Or perhaps it takes a noncomedian of “Gigli”-esque dimensions to finally sink this once-sparkling ensemble comedy.

• “PrimeTime” (9 p.m., ABC) introduces its new feature “That Was the Week That Was,” a tongue-in-cheek review of the week’s headlines. Other stories include Donald Trump’s business empire and female teachers who seduce their students.
• Meanwhile, back on planet Earth, “Wide Angle” (8 p.m., PBS) looks at two Colombian officials who risk their lives trying to assert their government’s authority in areas controlled by left-wing rebels and right-wing military groups, both of which are funded by that nation’s $6 billion-per-year cocaine trade.

Late night

Tom Cruise and Dax Shepard appear on “Late Show with David Letterman” (10:35 p.m., CBS) … Jay Leno greets Jude Law, Wanda Sykes, and Ciara and Petey Pablo on “The Tonight Show” (10:35 p.m., NBC) … Angela Bassett, Amanda Bynes and Maria Bamford appear on “Jimmy Kimmel Live” (11:05 p.m., ABC).

Gwyneth Paltrow, Paul Bettany and Drive By Truckers chat on “Late Night with Conan O’Brien” (11:35 p.m., NBC).