First base may be the position the Cubs are most secure at this season. For all of the bad things that have happened, Derrek Lee has been very productive. He leads the team in wins above replacement, at 3.5. He’s hitting .294/.374/.560, and after a somewhat down year in 2008 he’s raised his production back to pre-2007 levels. Yet it may be that the Cubs need to look at replacing him.

2010 is the last year of Lee’s contract, and he’ll turn 34 this weekend. And really, this season has shown us two Derrek Lees. In April he hit .189/.253/.284. It looked like his power outage from last season was set to continue, and that he was aging quickly. He managed just a single home run for the first month of the season. Since May 1, though, he’s hit .315/.398/.603 with 26 home runs. Just to give you an idea of how good those post-April numbers are, only three players in baseball - Albert Pujols, Prince Fielder and Joe Mauer - have produced that well over the full season.

But that April concerns me. After not hitting for power the second half of last season, Lee opened up the season demonstrating absolutely no power. It seems to be back now, but is it possible we could end up with another 80 or 90 game stretch where he can’t hit home runs? I don’t know, but that’s my concern.

Nonetheless, I think the Cubs go into 2010 with Lee as their starting first baseman. His value is higher now than it’s likely to ever be again, but he probably won’t be traded. He can veto a trade if he wants, and all indications are that he would do so. If he struggles I imagine he would give way pretty quickly to Jake Fox, whose glove wouldn’t do as much damage at first base as it would anywhere else. If he doesn’t struggle he can be a solid contributor, and his post-April season this year suggests that age hasn’t quite caught up to him yet. I think the Cubs will let Lee walk at the end of next season - not necessarily to give his job to Fox, who I’m certainly not sold on. But at 35 it will probably be time to say goodbye to him.

Still, for 2010, the Cubs will probably stand pat at first base, and that’s probably the right move - if Lee is, say, 75% as valuable next season he’ll still be about a 3-win player, and that kind of production would be hard for the Cubs to simply pull out of thin air.