The Chicago Bears are still experimenting with their starting offensive line.

On Thursday, Charles Leno saw first-team reps over Jordan Mills at right tackle, according to Brad Biggs of the Chicago Tribune. Mills worked with the second team before leaving practice early with what Bears head coach John Fox said was a calf injury.

The Bears selected Leno in the seventh round of last year's draft. The 6-foot-3, 302-pound Boise State product appeared in six games during the 2014 season (one start), serving mostly as an extra tackle in some run-heavy formations.

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Mills, on the other hand, is a former fifth-round draft pick who has started 29 games over the past two seasons. He was solid as a rookie but seems to have regressed since then.

(h/t Chicago Tribune)