McKnight became the third Chiefs player to tear his Achilles tendon when he was hurt in practice last week. He was coming off a two-touchdown game in a win in Miami.
Stephenson was suspended for the first four games of the regular season for violating the NFL's policy on performance-enhancing substances. That suspension ended with Monday night's 41-14 victory over the New England Patriots.
Chiefs coach Andy Reid said earlier Tuesday that he would wait to see Stephenson practice on Wednesday before he begins to decide whether he'll go back in the starting lineup.
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