Broncos center Tom Nalen will have another surgery on his left knee this week, calling into question whether he will be ready to play for the start of the season.

Coach Mike Shanahan described the surgery as a “clean-up,” and he said he hopes Nalen can go when the Broncos open the season on Monday night, September 8, at Oakland. But it sounds awfully optimistic to think that a 37-year-old coming off his second knee surgery of the summer will be ready to play in less than three weeks.

Nalen had arthroscopic surgery to repair torn cartilage in the knee in June. He participated in the first week of training camp, but soreness in the knee has kept him out of most training camp practices and both of the Broncos’ preseason games.

Nalen is heading into his 15th year with the Broncos. He has been relatively healthy for most of his career, starting all 16 games in 10 of his previous 14 seasons, including both of the Broncos’ Super Bowl-winning years, 1997 and 1998. But he was lost for the season with a torn right biceps in the fifth game of 2007, and now his 2008 season is getting off to a rough start.