Buffalo Bills defensive tackle Tyrone Robertson, inactive for each of the team's first four games this season, will sit out the next four as well because of a league-mandated suspension.

ESPN.com has learned that Robertson has been suspended four games for a repeat violation of the league's substance abuse policy. An announcement of the suspension is expected to be made this week.

A seventh-round choice in the 2001 draft, Robertson will not be paid during the suspension and the sanction will cost him $70,588 of his scheduled base salary of $300,000.

Robertson, placed on the Bills reserved-suspended list, is eligible to return to the active roster on Oct. 27.

To replace Robertson, the Bills activated linebacker Dominique Stevenson from their practice squad. Stevenson was the fourth of Buffalo's four seventh-round selections in last April's draft.

Robertson, 23, appeared in 12 games as a rookie and recorded 27 tackles, two sacks and one pass defensed. Buffalo coaches like the potential of the 6-feet-4, 295-pound Robertson, but have experienced problems in getting him to focus on football.

The former Hinds (Miss.) Community College standout, who started his college career at the University of Georgia, was fined several times last year for being tardy to meetings. The fact he had not dressed for a game yet this season was likely a reflection of his lack of maturity.

It is not known if the Bills will make a move to replace Robertson on their active roster.

Len Pasquarelli is a senior writer for ESPN.com.