Lawyers say testimony in Malaysian opposition leader Anwar Ibrahim's long-running sodomy trial could conclude as early as this week.

Anwar's lawyers Monday completed their defense case, in which they argued the charges were the result of collusion between Prime Minister Najib Razak and Anwar's chief accuser, a former aide who says he was sodomized in 2008.

The prosecution now plans to briefly call four witnesses to rebut key testimony presented by the defense. Thomas Hoogland, an orthopedic surgeon who has treated Anwar, testified that the Malaysian opposition leader suffers from back problems that make it unlikely he could have performed the sexual act of which he is accused.

Lawyers say testimony from the four witnesses will likely end the current phase of the trial, which has been under way since February 2010. The lawyers will then take several weeks to submit written summaries of their arguments before the court renders its judgment.

Anwar heads an opposition coalition that made major gains in Malaysia's last election, and is preparing for new elections expected early next year.

He was previously convicted of sodomy in 1998 but the conviction was overturned in 2004.