BALTIMORE -- The off-again, on-again status of Clay Buchholz's next start is off again, and Boston Red Sox manager John Farrell acknowledged the team may place the right-hander on the disabled list with ongoing discomfort in his trapezius muscle in his neck area.

With an off-day Monday, Felix Doubront will pitch on regular rest in Tuesday's doubleheader, with the other starter still to be determined. Ryan Dempster will pitch Wednesday against the Tampa Bay Rays.

The earliest Buchholz will pitch is now Saturday in Detroit, Farrell said. He threw on Saturday and felt improvement, but not sufficient to make a start Tuesday.

Buchholz last started on June 8 against the Angels, and has made just two starts, totaling 11 2/3 innings, since May 22. He is 9-0 with a league-leading 1.71 ERA.

"He's not at a point physically where he feels like he can get on the mound tomorrow without the potential of setback and not irritate the trapezius muscle," Farrell said. "The AC joint has cleared up. There's nothing there. It's more the trapezius muscle up in the neck that is restricting him from greater intensity.

"The bottom line is ... we're not going to put him out there without making sure he's in a safe place physically."

If there is not sufficient improvement by Tuesday, Farrell said, the Red Sox will consider placing him on the DL, retroactive to June 9. That would rule him out from starting before June 25 against Colorado.

Meanwhile, the team sent first baseman Mike Napoli back to Boston Saturday to undergo testing to determine the cause of dizziness, grogginess and light-headedness he has been experiencing since Thursday, when he came out of a game against the Rays in the third inning.

The Red Sox have consulted a concussion specialist who has all but ruled out that as a cause, Farrell said, but the club remains puzzled by his condition.

"He's improved," Farrell said, "but he still has some of the grogginess, symptoms he was feeling the other night. As a result we've sent him back to Boston to go through an examination to get more information on what he's dealing with."

That exam was to take place Saturday, Farrell said, by a team internist. Whether Napoli needs to see other specialists will be determined at that time, but the Red Sox have already consulted with MLB concussion specialist Micky Collins, and the club has a "pretty high level of confidence" that a concussion is not involved.

"There has been a virus running through the club," Farrell said. "A couple of guys threw up yesterday but still played. But we feel because this has persisted since the other night, we want to make sure he's in a safe place and we can get to the bottom of this."

Mike Carp started at first base in Napoli's place Saturday. Third baseman Will Middlebrooks also has taken ground balls at first the last two days.

"We had Will taking ground balls there yesterday in the event some in-game matchups, situations take us to where we need another right-handed hitter on the field," Farrell said. "We're adjusting as we go."