DETROIT — It has been almost one month since the Detroit Tigers sent Dontrelle Willis to Class A Lakeland to work on his control.

Willis has appeared in only one game there, against Daytona nine days ago. He allowed one earned run—on one hit and three walks—in two innings.

It's not known when he will be healthy enough to pitch again.

Willis was scheduled to return to Detroit early this week to have his right knee examined, the team said Monday. That is the same knee he hyperextended in April, forcing him onto the disabled list for the first time in his big-league career.

The setback reduces the chance Willis will pitch again in the majors this season.

Left-hander Willis, 26, has had a turbulent first season with the Tigers, after arriving in a trade with the Florida Marlins and signing a three-year, $29-million contract extension.

He is 0-1 with a 10.32 ERA in the big leagues this season. He was sent to Lakeland after allowing eight earned runs in a June 9 start against Cleveland.

Hollimon for Santiago: As expected, the Tigers sent infielder Michael Hollimon to Triple-A Toledo to make room for Ramon Santiago, who is expected to be in uniform at Comerica Park Tuesday night.

Santiago has spent a little more than one month on the disabled list after separating his left shoulder in early June. Santiago is known for his defensive ability at shortstop, and his playing time there could increase if veteran Edgar Renteria continues his hitting slump.

Santiago batted .083 (2-for-24) during the first seven games of his rehabilitation assignment at Toledo.

Detroit manager Jim Leyland praised Hollimon in recent days. Hollimon batted .261 with one home run and two RBIs in 11 games.

Prospect returns: In a development that could have ramifications for the Tigers' 2009 roster, shortstop Brent Dlugach has returned to game action with the team's Gulf Coast League affiliate.

Dlugach, 25, impressed Leyland during spring training last year and was a candidate to be called up to the majors until a shoulder injury ended his season in May.

If he stays healthy, it's not out of the question that Dlugach, a smooth fielder, will compete for a big-league role next year.

"The biggest thing," Tigers director of player development Glenn Ezell said, "is that he's on the field."

Olympic candidates: Dan Lunetta , the Tigers' director of minor league operations, said Toledo infielder Mike Hessman and Toledo closer Blaine Neal are under consideration for the U.S. Olympic team. ... The Tigers will honor U.S. Citizenship and Immigration Services with a pregame ceremony Wednesday. Detroit second baseman Placido Polanco, a native of the Dominican Republic, will be among 100 people sworn in during a service, the team announced.