According to ESPN's Adam Schefter, a source told him that Manziel "was heavily hung over on something" on the same day another report said he came to a late-season practice drunk and the Browns covered up the incident.
NFL Network's Mike Silver took to Twitter on Tuesday to stand by his report last week that Manziel showed up drunk for a late-season practice, but said he regretted saying the Browns lied about Manziel having a concussion.
The Browns issued a statement Tuesday reiterating that Manziel was in the league's concussion protocol.
"Johnny Manziel came to our facility on the morning of December 30th and complained of concussion symptoms," Browns said in the statement. "He was tested by an independent neurologist and entered the league's concussion protocol. He remained in the protocol until January 12th after being cleared by the independent neurologist."
Manziel reportedly was in Las Vegas on the Saturday night before the Browns' final regular-season game despite being in the concussion protocol that sidelined him for the game against the Pittsburgh Steelers on Jan. 3. He missed his mandatory concussion treatment on game day at the team's facility and was fined.
One well-placed Browns source who had contact with Manziel on Dec. 30 told Schefter: "Manziel looked terrible. He wasn't drunk, but he was heavily hung over on something. There was something going on there."
Manziel complained that he was having trouble with light, was vomiting and had a headache, according to ESPN.
"This wasn't some massive cover-up," the source told Schefter. "What are you going to do? You have to put him in the protocol.
"... He was not drunk that day, but he was (recovering) from being on something. I don't know what he was doing the night before, but something was wrong with him."
A Browns player told ESPN that several teammates knew Manziel had complained of headaches early that week, and that Manziel had briefly attended a quarterbacks meeting early that morning.
Another ESPN source had said Manziel arrived late for a meeting that Wednesday looking "disheveled" and that the team got him out of the meeting before putting him on the concussion protocol.
Manziel is being investigated on allegations of domestic violence due to the incident that occurred in the early morning hours of Jan. 30.
Dallas police announced last Friday that they will investigate a domestic-violence assault complaint against Manziel.
Manziel's now former girlfriend, Colleen Crowley, gave a statement to police and asked the district attorney to pursue charges, according to WFAA-TV in Dallas.
Her lawyer told a Dallas TV station on Monday that Manziel punctured Crowley's eardrum when he struck her and that it will take a while to regain her hearing in that ear.
Manziel's agent parted ways with the quarterback last week in the wake of the latest news, and Manziel's family has been concerned for his well-being. His father, Paul, told the Dallas Morning News last week that his son won't "live to see his 24th birthday" if he doesn't get help.
Manziel, who is from Tyler and Kerrville, Texas, told TMZ Sports last week the incident with his ex-girlfriend "didn't happen. I'm completely stable. I'm safe and secure."
Multiple reports indicate that Manziel will be waived by the Browns on March 9 when the new league year begins.
The Browns selected Manziel with the No. 22 pick in the 2014 draft. Cleveland has the No. 2 overall pick in the upcoming NFL Draft.
Manziel finished his second season with 1,500 passing yards, seven touchdowns and five interceptions in nine appearances (six starts) and a passer rating of 79.4. He rushed for 230 yards.