Michael Weatherly on leaving 'NCIS' for 'Bull': 'I was ready for a new challenge'

Michael Weatherly left NCIS in May after 13 seasons, but he won't be gone from the CBS schedule for long.

The actor returns to the small screen this fall as the star of the network's rookie legal drama Bull.

"It came about at the right time, I wasn't burn out by NCIS and I was ready for a new challenge," Weatherly told reporters Wednesday at the Television Critics Association summer press tour. "Sometimes change is as good as a rest."

Bull is based on the early career of Dr. Phil McGraw during his days as head of one of the most prolific trial consulting services of all time. Weatherly portrays Dr. Bull, the head of a company that analyzes juries to help develop defense strategies.

See photos of Michael Weatherly through the years:

(Although the series is on based on McGraw's previous line of work, the team downplayed comparisons between the character and the real daytime star. "It's not autobiographical, its not biographical, its inspired by," McGraw, who is also an executive producer, said. "This is fiction.")

Weatherly admits he was "really tired" from the grind of doing 22-episode seasons for the past 13 years, but the network pursued him nonetheless for Bull.

"I think CBS was really eager to keep Michael for the obvious reasons," executive producer Paul Attanasio said. "There is nothing in entertainment like a star in a star part."

The series executive producers were also unsure of whether he would be willing to do a broadcast series. "I was skeptical he was going to want to go sign up again because it's a hard job to do broadcast television, especially to be No. 1 on the call sheet is a nonstop job but he got excited about the part," Attanasio said.

See photos of Michael Weatherly on "NCIS":

Weatherly was soon approached -- "I said, 'I don't drink Red Bull,'" he quipped about the first receiving the script – and officially signed in March. "Bull is a big show with a lot of characters. Its complex. I solve problems the same way as an actor but it really requires a lot of different muscles."

Another big change? "I have to say its also a relief not to have wear a gun everyday," he said with a laugh.

However, for their many differences, Weatherly also sees at least one similarity between Jason Bull and Tony DiNozzo. "DiNozzo was a guy who [wanted] validation and approval and was very hungry for that and Bull is not hungry for that," he said. "He doesn't need that but both characters are fascinated by human behavior."

Weatherly's talent for comedy that became a cornerstone of his NCIS character will also be put to use on Bull. "He's got fantastic comic timing," Attanasio said. "And then he's just really good with dialogue and writers inherently like actors that can do lines and Michael can really do lines."

McGraw also praised Weatherly's casting: "It's just an absolute home run."

Bull premieres Tuesday, Sept. 20 at 9 p.m. on CBS.