BEREA, Ohio -- The Browns fear Myles Garrett's right ankle injury is serious, sources tell cleveland.com, and he'll undergo an MRI soon.

Garrett, the No. 1 overall pick, suffered the injury during Wednesday's practice and had to leave early. He didn't return. It occurred during the portion of practice closed to the media.

"He went as long as he could,'' said Jackson, in a somber tone.

Jackson acknowledged that Garrett's status for the opener Sunday against the Steelers is in doubt.

"We'll see where we are as we move through the week," he said.

The Browns won't know the extent of the injury until the results of the exams are in, but one source said the club fears he could miss a period of weeks, possibly four or more.

The Browns might also solicit a second opinion, as they did when Garrett suffered a lateral left foot sprain during minicamp on June 14. In that instance, Cam Erving stepped on Garrett's left foot on his way to a would-be sack of Brock Osweiler.

The Browns had foot specialist Dr. Robert Anderson of OrthoCarolina review the MRI films of that injury, and he confirmed team physician Dr. James Voos' diagnosis. Garrett was sent home in a walking boot and stayed off the foot for a few weeks.

Garrett also suffered a high left ankle sprain that hampered him last season at Texas A&M, where he was limited to 8.5 sacks.

After the minicamp sprain, Garrett returned healthy for training camp, but he was eased into practice for precautionary reasons. Garrett made it through camp and three preseason games before the injury occurred on the first full day of preparation for the Steelers.

The loss of Garrett for any length of time would be a huge blow, especially considering the Browns play their three AFC North foes in the first four weeks.

News of his injury came hours after Garrett backed up his draft-day remarks that he was coming to 'chop down' Ben Roethlisberger.

He said "you can't be scared to take somebody down."

Former Browns cornerback Joe Haden, who signed with the Steelers last week, knows how important Garrett is to the defense.

"He's looking like the first overall pick,'' Haden said on a conference call Wednesday. "I was super excited when we got him. I feel like that's the pick that is a stamp. We didn't miss on that one. I could tell that from the very beginning. He just has stuff that you can't teach - his motor, his professionalism and his attitude.

"He definitely is a pro already. He is mature beyond his age. He just loves the game and loves getting after it. My bold prediction, I really feel like Myles can make the Pro Bowl his rookie year."