Greg Colbrunn remains in hospital

DETROIT -- Boston Red Sox hitting coach Greg Colbrunn remains hospitalized in Cleveland but his condition is improving two days after being diagnosed with bleeding in the brain, according to manager John Farrell.

Colbrunn was taken to the Cleveland Clinic before Wednesday's game with the Cleveland Indians. Bleeding in the brain is potentially a life-threatening condition.

"I've been talking to his wife today and there's been some improvement," Farrell said before Friday night's game against the Tigers. "He's walking around. He will remain in the hospital for at least a week."

Colbrunn, who was taken to the clinic after experiencing dizziness, was diagnosed with subarachnoid hemorrhage. According to the UCLA neurosurgery website, SAH, as it is known, involves bleeding into the space between the surface of the brain and the arachnoid, which is one of three coverings of the brain.

"Trauma is the most common cause of spontaneous SAH, and 75 percent to 80 percent of spontaneous SAHs involve ruptured brain aneurysms," the website says. "Other causes of SAH include arteriovenous malformation (AVM), vascular inflammation affecting the central nervous system, and carotid artery dissection."

Farrell said that Colbrunn was complaining of a headache before he went to Progressive Field in Cleveland on Wednesday and the pain worsened.

There is no timetable for when Colbrunn might rejoin the team.

"We're hopeful he will return to us," Farrell said, " ... but now his health is first and foremost in our minds and the rest will work itself out."

Red Sox assistant hitting coach Victor Rodriguez will assume Colbrunn's responsibilities and minor league hitting coordinator Tim Hyers will serve as assistant hitting coach for the time being.

"Greg is stable," Red Sox general manager Ben Cherington said. "We have a good prognosis and obviously in really good hands with the people there at Cleveland Clinic. He'll likely be in Cleveland for a few more days. Everything we've heard is that there's a very optimistic prognosis and that he's doing well. Obviously all of our thoughts are with him, his wife Erica and his family. We know he's getting really good care. Beyond that, there's not much more I can say. It's looking good and everyone is optimistic about a full recovery."

Cherington said the Sox will seek to supplement their coaching staff while Colbrunn remains out by having Hyers help the big league team.

"At this point, we do expect Greg to rejoin the team but it's just too early to say when," Cherington said.

Information from ESPNBoston.com's Gordon Edes and contributor Kyle Brasseur was used in this report.