DENVER -- Broncos wide receiver Wes Welker, who missed three games last season after sustaining two concussions, has been diagnosed with another one.

Broncos coach John Fox said Welker suffered a concussion during the team's 18-17 loss Saturday night to the Texans. Welker left the game following a hit to the helmet from Houston safety D.J. Swearinger.

"It was determined it was a concussion," Fox said. "He'll go through the protocol. The biggest thing on him is, of course, player safety. He'll go through the protocol."

In terms of a timetable for Welker's return, Fox said that will be determined by doctors.

"We'll leave that to the medical people and he won't come back until he's ready to come back," the coach said.

The play came in the waning seconds of the opening half. The Broncos, after a Texans punt, took over on their own 36-yard line with 32 seconds remaining before halftime.

Welker caught an 11-yard pass from quarterback Peyton Manning to move the ball to the 47. On a first-and-10, Manning hit Welker again in the middle of the field, and, as the receiver lunged forward, Swearinger hit him in the head.

Replays appeared to show that, as Welker's head dropped as he began to slide, Swearinger hit him with a combination of forearm and shoulder. Welker got up on his own but immediately waved to the Broncos' trainers to come on to the field.

"I led with my shoulder; that's the only thing I can do," Swearinger said. "He's a short guy. I led with my shoulder. The results are the results and that's all I can do on that play."

Welker got up and walked next to a member of the Broncos training staff, went off the field and straight into the locker room.

Swearinger was assessed a personal foul for a blow to the head and later said he was surprised to see a flag thrown on the play.

"The NFL is the NFL," he said. "They want it how they want it. I gotta play ball how I'm gonna play ball."

On the next play, Manning hit Emmanuel Sanders for a 29-yard touchdown, and Manning then ran all the way into the end zone to confront Swearinger. Manning was flagged for taunting. The Broncos said that was apparently the first such penalty in the five-time MVP's career.

Wes Welker, who has a history of concussions, left after taking a hard hit to the helmet by the Texans' D.J. Swearinger, left. AP Photo/Jack Dempsey

"Peyton was mad," Swearinger said. "He gave me some choice words on that play."

Manning said he was upset about the hit given Welker's history.

"Obviously concerned about Wes, I just didn't like seeing him come out of the game, a potential blow to the head, that kept him out a while last year, so obviously concerned about him," Manning said.

Welker, who caught 73 passes for 10 touchdowns and 778 yards in 2013, suffered two concussions last season and missed the Broncos' final three games of the regular season.

He returned for the Broncos' three playoff games, wearing a helmet with extra padding. Welker has continued to wear the helmet this season, as well.

Welker was not scheduled to play in Thursday's preseason finale in Dallas against the Cowboys, but his availability for the Sept. 7 season opener will be dependent on whether he is cleared by both the team's medical staff and an independent doctor who has been approved by the NFL and the NFL Players Association under the concussion protocol.

ESPN.com Texans reporter Tania Ganguli and The Associated Press contributed to this report.