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12/18/2013 5:25 P.M. ET

Phils invite additional four players to Spring Training

PHILADELPHIA -- The Phillies have invited four more players to Spring Training as non-roster invitees: outfielder Tony Gwynn Jr., catcher Lou Marson, right-hander Sean O'Sullivan and outfielder Dave Sappelt.

The quartet joins right-handers Shawn Camp and Jeff Manship; left-hander Cesar Jimenez; infielders Andres Blanco and Reid Brignac; and outfielders Leandro Castro and Clete Thomas.

Gwynn hit .300 with a .393 on-base percentage, 12 doubles, five triples and 27 RBIs in 333 at-bats for Triple-A Albuquerque last season. He has hit .244 in 605 games with the Brewers, Padres and Dodgers.

The Phils selected Marson in the fourth round of the 2004 First-Year Player Draft before trading him to the Indians in July 2009 in the Cliff Lee deal.

O'Sullivan went 8-5 with a 3.83 ERA in 20 starts last season with Triple-A Tucson. He also appeared in seven games with the Padres, including three starts, going 0-2 with a 3.96 ERA in 25 innings. O'Sullivan has a 5.89 ERA in 218 2/3 innings in 50 big league games.

Sappelt hit .240 in 31 games with the Cubs and .252 in 90 games with Triple-A Iowa.

Mizerock brought on as assistant hitting coach

PHILADELPHIA -- The Phillies announced they have hired John Mizerock to be their assistant hitting coach.

Mizerock, 53, spent the past three seasons as a coach with Class A Clearwater. He spent the previous 17 seasons in the Royals organization, including five years as bullpen coach (2002, '08-09) and third-base coach ('03-04).

"John has a lot of experience in the Major Leagues," Phils general manager Ruben Amaro Jr. said. "He was working with our catching and has done a good job with guys coming through, like Cameron Rupp. He is a knowledgeable guy and very good employee. He knows the game and understands the game."

Mizerock's addition completes manager Ryne Sandberg's coaching staff: Larry Bowa (bench), Steve Henderson (hitting), Pete Mackanin (third base), Bob McClure (pitching), Mizerock, Rod Nichols (bullpen), Juan Samuel (first base) and Jesus Tiamo (bullpen catcher).

Worth noting

• The Phillies offered former manager Charlie Manuel a job in the organization several months ago, but they are still waiting for an answer.

"We're still talking to Charlie about that possibility," Amaro said. "[We] haven't made anything official yet, [but we're] hoping to bring him back. [We are] looking to have someone who can help us in a variety of roles. He could be a hitting guru with the organization -- troubleshooting and scouting, much like he was when he was here for Ed Wade. I hope he comes on and will be a tremendous asset for us. I think he can help us and me in a variety of ways."

• The Phils designated catcher Sebastian Valle for assignment to make room for right-hander Roberto Hernandez on the 40-man roster.

Valle had been the organization's top catching prospect just a couple of years ago, but he had fallen on the depth chart. He posted a .699 OPS in 2012 with Double-A Reading and Triple-A Lehigh Valley, and just a .603 OPS last season with Reading.

"Prospects are prospects," Amaro said. "Sometimes they develop, sometimes they don't. He didn't develop at the rate we thought he would. We're fortunate that we've had others that have stepped up. ... And having signed [Wil] Nieves, I think will give us some depth on the Major League club."

Todd Zolecki is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.