[MLS CUP PLAYOFFS: Preview] The four conference semifinals to be played Wednesday and Thursday all present difference scenarios, yet three of them feature one common thread. At least one important player’s participation is clouded by injury, and the depth that coaches and executives always talk about will be put to the test.

But for several teams, simply plugging in a replacement may fill a hole but may not address a need. The four first legs all finished with different scorelines and thus the decisive matches are of four different shades.

DEEP HOLE FOR SKC. Sporting Kansas City is down 2-0 to Houston from the first leg and may be missing holding midfielder Julio Cesar, who suffered a quadriceps injury against the Dynamo. Coach Peter Vermes could normally turn to veteran Paulo Nagamura for Wednesday’s second leg, but he is hobbled by a sprained right ankle. Thus there’s a large midfield void as SKC tries to wipe out a two-goal deficit, which it did in 2004 en route to its last MLS Cup appearance.

Vermes does have myriad options for the second leg (9 p.m. ET, MLS Direct Kick), starting with Lawrence Olum, who played a few impressive games at centerback and also has experience at central midfield. He could also use Peterson Joseph to add some energy.

The key for SKC, however, is to free up Graham Zusi, the MLS leader with 15 assists who has looked jaded since returning from U.S. duty in the middle of October. If more attacking oomph is needed, Vermes could give a start to Bobby Convey -- who came on as a sub in the final minute of the first leg -- on the left and use his slashing runs to free up Zusi and also get more service to C.J. Sapong and Kei Kamara.

If ever the cliché of “needing an early goal,” applies, it is in this situation. SKC can score the needed goals and has the resilient defense to stay in the game. Its task will grow more daunting the longer it takes to break through and how Vermes deals with Julio Cesar’s absence will play a pivotal role in the outcome.

Zusi believes SKC learned some valuable lessons last year, when it lost at home to Houston, 2-0, in the conference final.

“I think it was kind of an experience thing,” he says of a squad a bit short on postseason play. “You look at the team from last year; a lot of those guys, including myself, hadn’t really been in that position before. “If you see us put in that position again I think you’ll see us come out on the other end.”

RAFA REFERENDUM. For its second leg against D.C. United (8 p.m. ET, NBCSN) with the series tied,1-1, New York is dealing with yet another injury to defender Rafael Marquez. He departed with a calf strain at halftime of the first game, though Coach Hans Backe said after training Tuesday that Marquez’s chances of playing in game two were “as much as 90 percent.”

While a significant portion of Red Bull Nation believes its chances of success vary inversely to Marquez’s participation, Backe obviously feels the central pairing of Markus Holgersson and Marquez is his best option. Heavy rains and high winds are likely with a ‘noreaster expected to lash the stadium, which increases the risk of fielding a gimpy player. It also ratchets up the possibility of costly mistakes after defensive gaffes produced own goals by either team in the first leg.

Regardless of conditions, attacker Tim Cahill  -- who sat out the first leg with a calf injury -- has declared his intent to play. The veteran of many Premier League seasons with Everton knows his way around on a sloppy field with everything on the line.

“It’s all about managing and I’ve had enough experience in how to manage injuries and how to get through games, and a few times this season a few of us have done,” he told mlssoccer.com. “It’s a significant injury, but it’s a big game and I don’t like missing big games.”

CALI CLASICO, PLAYOFF STYLE. As of Tuesday, San Jose and Los Angeles hadn’t reported significant injuries for their second leg Wednesday at Buck Shaw Stadium (11 p.m. ET, ESPN2).

This game, the fifth played between these bitter rivals this season, doesn’t need additional layers of intrigue. David Beckham says his departure in the 78th minute wasn’t due to any injury but rather to rest him for the second leg, which is the Galaxy’s third postseason match in seven days.

San Jose struck in stoppage time Sunday to score a fourth consecutive goal against the Galaxy on a set play. Predictably, Coach Bruce Arena complained about the foul call that yielded the free kick that defender Victor Bernardez drove low into the Galaxy’s defensive wall.

The ball caromed off Omar Gonzalez’s foot and squirmed under the arms of keeper Josh Saunders, who owned up to his error. Taking a 1-0 lead into a decisive home game hasn’t clinched anything, according to the San Jose players and coaches.

“We can’t think that we have a lead,” said Golden Boot winner Chris Wondolowski prior to a training session Tuesday. “It’s only halftime. We are going to pick and choose our spots to get after them. We want to stay organized but we also think that the Galaxy will leave some gaps open that we can get at them, especially on the counterattack.”

EJ SET TO GO, ROSALES TBA. Seattle playmaker Mauro Rosales sat out the first leg against RSL Friday, a 0-0 tie, and his ouchy hamstring has his status for game two in doubt (Thursday, 10 p.m. ET, NBCSN). The Sounders generated several quality chances in the first leg but were denied by a brilliant Nick Rimando.

Rosales sat out last year’s playoff series against RSL, which prevailed, 3-2, on aggregate. The Sounders’ struggles against RSL this season are nearing inconceivable: they haven’t scored in four games and three of them have been scoreless ties.

Seattle’s odds of finally breaking through can be helped by the return of Eddie Johnson, who left the season finale against the Galaxy with a hamstring strain that sidelined him for the first leg. In the 20 games he started up top with Fredy Montero, their combined totals were 18 goals and 10 assists.

“His presence opens up space for Fredy Montero and Fredy Montero’s presence opens up space for Eddie,” said Coach Sigi Schmid said to mlssoccer.com. “He hasn’t scored 14 goals for no reason and Fredy hasn’t scored 13 goals for no reason. With each other, they are a very formidable duo and they help feed off each other.”

Depth is one reason the Sounders have found success in outside competitions: four straight Open Cup final appearances, and earlier this year advancement to the quarterfinals of the CONCACAF Champions League. It needs more of the same to end its playoff frustrations.