Mid-April 2011 marked the Timbers' first in-season acquisition of the MLS era (DP Diego Chara, signed April 13), but the team still had two MLS trades ahead, acquiring instant starters LB Mike Chabala and RB Lovell Palmer in July, and midfielder Eric Alexander in August.

So while worries about the team's defensive performance have already expressed themselves in the form of two veteran international trialists, why wouldn't the front office be actively pursuing an MLS trade to upgrade the back line? If so, which players look most likely to be on the block?

Here's a look at six of them (based on potential trade value and depth at their position, with a bonus for international players whose departure would open a slot), plus a throw-in.

Kalif Alhassan: After a red-hot start displayed his undeniable skill over the ball, Alhassan was sure to attract attention from other clubs (including transfer attention from other leagues). But despite his talent and youth, Alhassan has been an inconsistent and occasionally problematic player. He's also recovering from a slight injury, but his trade value is high. Depth on the wing: +1. International: +1.

Jake Gleeson: Considered a high-potential young player on the rise, he's also injured, subject to international call-up, and a benchwarmer behind Troy Perkins. With Joe Bendik suddenly also injured, the Timbers could use a new backup keeper. Depth: Meh. International: +1.

Eric Alexander: A smart and versatile midfielder with international experience, Alexander's play has already attracted trade inquires from three teams in 2012. Depth: +1. International: -1.

James Marcelin: A talented, physical, young defensive-minded midfielder, Marcelin is the development project behind Jewsbury. After a good preseason, his season has been undistinguished. Trade value is moderate to meh. Depth is poor. International: +1.

Andrew Jean-Baptiste: A big Generation adidas rookie with outstanding developmental potential, he's played above modest expectations as a fill-in starter. Probably enough to attract teams that see a chance to trade a competent but fading fullback for a future star at centerback. Trade value is good, depth will be good once Horst and Futty return to full strength. International is a -1.

Rodney Wallace: An athletically gifted outside defender who plays more like a midfielder, Wallace is a controversial player who might attract attention from the right style of team. But his trade value is low, the depth at his position is terrible, and it's hard to imagine a great scenario for him. Listed here only because there could always be that one GM out there who sees a future MLS all-star in Wallace. International +1.

Lovel Palmer: Much maligned during the past week, Palmer has done some good things for the Timbers, but he's probably no better than a journeyman. More likely to be cut than traded, if only because he soaks up an international slot. Could be included in a trade.