Tom Arnold, fresh off his ratings triumph with ABC’s “The Jackie Thomas Show” on Tuesday, will get a major promotional platform this weekend … from NBC.

Arnold has been booked as host of “Saturday Night Live”– subbing in for late scratch Gary Oldman, and in the process ruffling some feathers over at NBC Entertainment.

Sources say Oldman backed out on Monday and Arnold was booked by “SNL” exec producer Lorne Michaels shortly thereafter.

The news apparently reached West Coast NBC executives on Wednesday–just about the time they were getting national ratings for “Jackie Thomas,” which hung on to 90% of its lead-in to score the highest post-“Roseanne” half-hour in more than nine months and the top new series rating in over two years.

While it’s not unusual for “Saturday Night Live” to feature hosts from shows on other networks, such as Candice Bergen and Jason Priestley, the timing of Arnold in such proximity to “Jackie’s” premiere produced “some head-scratching” in the halls of Burbank, an NBC source acknowledged–particularly with the on-air promotion afforded to “SNL” and the importance of week two in terms of how well “Jackie” sustains its introductory numbers.

Michaels reportedly was left scrambling for a host after Oldman dropped out, and NBC staffers say the scheduling could have a small upside, at least, if it produces a big rating for “SNL.”

Roseanne Arnold is expected to appear on this weekend’s show but won’t co-host. The Arnolds also produce “Jackie Thomas” in association with Lorimar TV.

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