NASHVILLE, Tenn. -- Tennessee quarterback Jake Locker is out with a hip injury, and coach Mike Munchak doesn't know for how long.
One thing is certain. It couldn't have come at a worse time for the Titans or Locker.
The coach said Monday that Locker will have another MRI exam Tuesday to diagnose the extent of the injury he suffered Sunday against the New York Jets. The test will give the Titans a better idea of when he can return.
Tennessee (3-1) is off to a surprising start after going 6-10 last year behind Locker, who is playing the best football of his career.
Munchak remained optimistic Locker will be back this season and said any reports on how much time Locker will miss is simply guessing now because the Titans haven't discussed the possibilities with the quarterback yet.
"He still has swelling so they don't want to speculate on terming what that means or how long and rehab and how long this all will take," Munchak said. "He'll be MRI'd again tomorrow, then we'll have a better idea exactly what the time frame before he can actually play or get back on the field."
Munchak said Locker also sprained his right knee on the hit.
Ryan Fitzpatrick now will replace Locker in Sunday's game against Kansas City (4-0).
The coach did not rule out a fracture or dislocation until after the next tests. Munchak dismissed reports earlier Monday that Locker will miss at least a month, saying that determining the severity of an injury can be difficult early. He also said the Titans will announce how long Locker is out after Tuesday's tests.
"Then we'll have to make some decisions and see exactly where we're at," Munchak said.
The Titans signed Fitzpatrick in March to a two-year deal, and right now he's the only other quarterback on the roster. Rusty Smith, a four-year veteran, currently is on the practice squad. Smith said he hadn't been approached yet about being promoted to the roster or heard if the Titans might sign someone else to back up Fitzpatrick.
Locker spent the night in the hospital after being injured early in the third quarter of a 38-13 win over the Jets. Locker was hit first by Muhammad Wilkerson and pinballed off Quinton Coples before grabbing at his hip as he went to the ground. Munchak said Locker couldn't pull out his foot with his hip caught in a kind of whiplash effect.
Munchak talked with NFL officials Monday about the hits.
"The first one was he dropped his helmet into him and unloaded on him, which you're supposed to pull back when you're late. The second one was totally unnecessary," Munchak said.
Locker was released from the hospital Monday morning and had treatment at the Titans' headquarters before going home.
"I want to thank everyone for their thoughts and prayers over the last 24 hours," Locker said in a statement released by the team. "I am going to work as hard as I can to get back as soon as I can. I believe in this team and will do whatever I can to help us win in the meantime."
He missed five games last season because of an injured left shoulder. The timing of this injury is much worse.
Locker currently is the third-ranked quarterback in the AFC by passer rating behind Denver's Peyton Manning and Philip Rivers of San Diego. Locker currently has a 99 passer rating and is completing a career-high 62.2 percent of his passes with six touchdowns and no interceptions.
The Titans (3-1) are off to a strong start after going 6-10 last season. They wrap up a three-game home stand against the Chiefs on Sunday before visiting Seattle (4-0) on Oct. 13. They host San Francisco (2-2) before their bye in a stretch that looked challenging even before Locker was injured.
If Locker missed only a month, he would be on target to return Nov. 3 when Tennessee visits St. Louis.
Fitzpatrick helped Buffalo start 5-2 in 2011 and signed a big extension with the Bills. But he went 1-8 down the stretch and was 6-10 last season before Buffalo released him on the opening day of free agency in March after a coaching change.
Now the veteran with 81 interceptions in eight previous seasons takes over an offense that has not turned the ball over even once through the first four games, something only the 1995 St. Louis Rams have done in the Super Bowl era.
"We've already made that point clear to him that we need to keep the record going," Munchak said. "It's all on him and his shoulders to come in and be good with the football."
Notes: The Titans hope RB Shonn Greene, who has missed three games with an injured right knee, and DT Sammie Hill (right ankle) can do some individual drills this week. WR Kenny Britt, who sat out against the Jets with a cracked rib and sore neck, is expected to practice Wednesday.