Wisconsin running back Montee Ball was attacked by five unknown assailants early Wednesday morning.

CBSSports.com has learned that Ball sustained a concussion as a result of the attack.

Additional details of the assault are still sketchy, but according to the police report Ball was attacked by five men while walking down the 500 block of University Avenue. Witnesses say the five men jumped Ball and knocked him to the ground before they began kicking him.

According to police spokesman Joel DeSpain, witnesses said Ball may have exchanged words with the men before they attacked him. The motive for the attack remains a mystery. Ball told investigators his cellphone is missing, but it's unclear whether the attackers stole it or someone just happened to pick it up.

"We're going to take a look at whether the victim was targeted for who he is," DeSpain said. Ball, a Heisman Trophy finalist last season as a junior, was taken to a hospital with head injuries, police said. Wisconsin coach Bret Bielema said Ball was released and under the care of the school's sports medicine staff.

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"My concern right now is for Montee's health and well-being," said Bielema. "Montee has been released from the hospital and is under the care and supervision of our sports medicine staff. We will continue to evaluate him as we approach the start of fall camp this weekend. I do expect Montee to make a full recovery.”

Bielema said that Ball will not be ready for the start of Wisconsin's preseason camp on Monday.

The Wentzville, Mo. native took to his Twitter account to deliver a message to the fans, confirming the expectation of a full recovery. 

Ball was a Heisman Trophy finalist for the Badgers in 2011, finishing the season with 1,923 rushing yards and 39 total touchdowns, leading Wisconsin to a Big Ten title and a Rose Bowl berth.

Information from the Associated Press was used in this report. 

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