The Giants hit the field Monday morning for their first practice in regular-season mode, their roster trimmed to 53. It was no surprise that 51 players were in uniform, with two of them, defensive end Osi Umenyiora and rookie cornerback Prince Amukamara, nowhere to be seen.

Umenyiora is coming off arthroscopic knee surgery on Aug. 19 for what the Giants called “a simple debridement’’ to clean out some cartilage issues in his right knee. He will not play in the Sept. 11 season-opener in Washington.

“It’s a little early,’’ Tom Coughlin said.

The initial timeframe for Umenyiora's return was 3-4 weeks although sources close to him put it at 4-6 weeks.

Amukamara is expected to miss the first month of the season with a broken foot.

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With the roster trimmed, a few Giants have changed numbers. Rookie linebacker Spencer Paysinger is No. 55, rookie running back Da’Rel Scott is 33, cornerback Brian Williams is 29, rookie tackle James Brewer is 79 and cornerback Derrick Martin is 22.