Red Sox general manager Theo Epstein accompanied the team back to Boston from Oakland late Wednesday night and could not be reached for comment.
On Thursday, the Red Sox issued a statement that Lester "has been undergoing testing to determine the cause of the back pain he has been experiencing." According to the club, while being checked out, several abnormally enlarged lymph nodes were identified. The statement went on to conclude that Lester "is resting comfortably."
The 22-year-old Lester was rear-ended in a car accident on Storrow Drive while on his way to pitch at Fenway Park on Aug. 18. Before and during his next start at Anaheim -- a win -- his back locked on him as he was dealing with an apparent case of whiplash.
When the Red Sox went to Seattle last weekend, Lester, a native of Tacoma, Wash., wasn't seen in the clubhouse during media access hours for the entire series.
A source confirmed to MLB.com that Lester spent much of the weekend in a Seattle hospital undergoing, among other things, a CT Scan.
Epstein offered no comment a few days ago when asked if Lester had been in the hospital while the club was in Seattle.
Manager Terry Francona did mention to reporters earlier this week that he had spoken with Lester's dad while the club was in Seattle, but that conversation was thought to have been regarding the pitcher's back.
The Red Sox, other than acknowledging Lester suffered whiplash, have not said anything about his condition. Due to his back woes, Lester was placed on the 15-day disabled list on Monday.
"He's obviously a big part of our future, and we've asked a lot of him already," Francona said Monday. "We're concerned about sending him out there when we shouldn't because we're thin. We don't want to hurt this kid. He's too valuable to our future."
Because of patient confidentiality laws, it is not surprising that the club would not discuss Lester's status until they determine exactly what is going on with left-hander.
There have been plenty of other health issues surrounding the Red Sox. Slugger David Ortiz checked in to Massachusetts General Hospital on Tuesday so doctors could determine why he, on multiple occasions over a 10-day span, experienced a rapid heartbeat. Ortiz, according to manager Terry Francona, is doing well, and was again held overnight on Wednesday as more tests were conducted.
Before the report surfaced on Lester, Red Sox ace Curt Schilling mentioned that the left-hander's situation, along with that of Ortiz, far transcends baseball.
"You're talking about David's health situation, Jonny Lester's situation and all the other guys," said Schilling. "It's bigger than wins and losses. Unfortunately, people can't look at it like that from a fan's standpoint a lot of times. But there's a lot of personal things going on here that are dragging on us a lot more than just the weight of losing these games."
The Red Sox have suffered a barrage of baseball injuries over the past few weeks, ranging from Manny Ramirez's right knee to Wily Mo Pena's left wrist to Alex Gonzalez's strained oblique. But those matters, as much as they've affected the way the team has played, are trivial compared to what is going on with Ortiz, and, apparently, Lester.
Lester is 7-2 with a 4.76 ERA in 15 starts this season. The Red Sox open a 10-game homestand against the Blue Jays on Thursday night.