According to TMZ

Kyle Glover -- 11-year-old son of Usher's estranged wife Tameka Foster -- is in critical condition in an Atlanta hospital after he was struck by someone riding a jet ski ... TMZ has learned. 

According to our sources, Glover was sitting in an inner tube on Lake Lanier when he was hit in the head. We're told Glover was unresponsive when he was taken out of the water. 

Our source say Glover remains unresponsive and is currently in critical condition. 

We're told that despite Usher's acrimonious divorce from Foster, he chartered a plane for Tameka, who was out of town, to be by her son's side. 

Our sources say she was extremely thankful for Usher's grand gesture and she rushed immediately to be by her son's side.

UPDATE

Usher's 11-year-old stepson has been declared brain dead by doctors following the accident yesterday when he was struck by a jet ski ... TMZ has learned. 

According to our sources, Kyle Glover (son of Usher's estranged wife Tameka Foster) has not experienced any brain activity since he was admitted to the hospital. We're told there has been no decision yet as to whether or not to take him off life support. 

Our sources say Usher arrived at the hospital last night and Tameka has not left the hospital since she got there. 

As TMZ first reported, Kyle was struck in the head by passing jet ski while riding on an inner tube on Lake Lanier in Atlanta, GA.

Our prayers go out to the entire family.

The Department of Natural Resource in Atlanta is investigating the accident that left Kyle Glover, stepson of R&B star Usher in critical condition ... an investigation which could take months to complete. 

As TMZ first reported, the 11-year-old was struck in the head by a jet ski while riding in an inner tube on Lake Lanier. He was rushed to a nearby hospital and remains there in critical condition. 

Robin Hill, a rep for the Department of Natural Resources (Wildlife Resources Division), tells TMZ the department's Critical Incident Response Team will recreate the accident on the lake to help determine what happened. Using special computer programs, they will attempt to figure out how fast the boats were going at the time of the accident. 

Hill says that rangers have been in touch with the driver of the jet ski and remain in contact with him. Once the department completes their investigation, they will turn their recommendation over to the district attorney who would then decide whether or not to file charges.