According to the AP: (emphasis mine)

Memphis senior reserve guard Andre Allen has been suspended for violating team rules, leaving him out of the Final Four.

Allen played in 37 games this season, averaging 3.3 points and 14.1 minutes.

"We'll be fine," coach John Calipari told The Commercial Appeal.

According to WREG-TV in Memphis, Andre Allen failed a drug test:

News Channel 3's Glenn Carver and Richard Ransom are both in San Antonio and learned four Tigers players were randomly drug tested. Allen reportedly failed his test.

Although he is only a backup PG, his removal could mean either (a) Rose will be forced to play all 40 min or (b) a even worse backup guard will be forced to play.  Secondarily, this means that the bench depth at point will be much lower for Memphis, giving us an opportunity to get Rose into foul trouble (although unlikely).

However, he was an important player in the previous two years, according to Commercial Appeal, a local Memphis news source

Over the past three seasons, Allen has been a key contributor in NCAA Tournament games. During the 2007 postseason, he averaged 21.7 minutes and was often playing point guard in late-game situations. In 2006, he was the Tigers' de facto point guard, even though he came off the bench during that team's Elite Eight run.

Previously, Allen was in trouble in 2005 for soliciting prostitution, though the case was dismissed.

In any case this doesn't change our preparation at all, and it doesn't change Memphis's preparation at all. However, I just want to point out how fortunate we are to have well-adjusted and mature players.