Seattle Seahawks cornerback Richard Sherman, who is appealing his four-game suspension for performance-enhancing drugs, has argued that his urine specimen was contaminated while being collected for testing, a league source told ESPN.

A major part of Sherman's appeal, which was heard Friday, involved his claim that the cup containing his urine specimen was leaking, prompting the collector to place a second cup underneath it to capture any leakage, the source said. A decision on the appeal is expected to be announced by Thursday, according to a league source.

Sherman stated that the second cup's seal already had been broken before being used to stop the leakage from his cup, according to the source. Since the second cup's seal was broken, the chain of custody also was broken, therefore nullifying Sherman's positive test for Adderall.

Sherman and his representatives argued that his tested urine sample was contaminated as a result of the second cup. If the collector confirmed the second cup's seal was broken, there would be grounds for Sherman escaping his suspension.

Sherman criticized the NFL's testing process Tuesday on Twitter.

"Hoping we play in a just League @nfl," he wrote. "Not a league that allows a tester to mix urine samples. A tester with a history of errors. Has has had to have 6 other tests thrown out and he has only been testing 6months."

A verdict is expected to be handed down this upcoming week, but Sherman was permitted to play in Sunday night's contest against the NFC West rival San Francisco 49ers.

"It should go well. There was a chain of custody mistake. There were mistakes made by the tester," Sherman said after the Seahawks' 42-13 win over the 49ers. "The league's argument was they're allowed to make mistakes and they're allowed to break the rules and they can get away with it. It's up to them. The appeal officer is paid by the league so if he goes their way, that's what it is. It's not an even playing field in that appeal room."

Sherman returned a blocked field goal for a 90-yard touchdown and had an interception in Sunday's win as Seattle clinched a postseason berth.

Sherman missed two days of practice this week while his appeal was heard, but any lack of preparation for the 49ers didn't show. Sherman had an interception, four passes defensed, and he returned a blocked field goal 90 yards for a touchdown in the Seahawks' blowout victory.

News of Sherman's suspension and that of fellow cornerback Brandon Browner broke after the Seahawks' loss at Miami on Nov. 28. Browner dropped his appeal on Dec. 5 and was suspended for the final four games of the regular season. Browner will return and be eligible to play for the Seahawks in the playoffs.

If Sherman's suspension is upheld, he would miss the playoffs. He said the process hasn't been a distraction.

"Not at all," he said. "I've faced worse than that throughout my whole life. Nothing little like that can hold you back."

Information from The Associated Press was used in this report.