Muhsin Muhammad, a wide receiver for the Carolina Panthers who roomed with Carruth, told jurors he and Carruth not only discussed the impending birth, but also the mother, Cherica Adams.
Prosecutors contend Carruth planned Adams's slaying to avoid paying child support.
He could face the death penalty if convicted.
Rae Carruth faces the death penalty in the 1999 murder of his girlfriend.(AP Photo)
"We talked about the fact that he did not have a bond with his child in California," Muhammad testified, speaking about Carruth's son from a previous relationship.
"He was excited about this opportunity to bond with this child."
Carruth said he wanted to remain good friends with Adams because he didn't want "any bad blood" that could harm his relationship with their child, he said.
Muhammad also disputed the state's claim that Carruth was worried about his financial future because he missed several games with an ankle injury prior to the Nov. 16, 1999, shooting of Adams.
"He's a first-round pick, single, with one son," Muhammad said. "I'm a second-round pick with a wife and two kids.
"I don't think Rae was hurting for any money."
Adams, 24, was eight months pregnant with Carruth's son when she was shot.
The baby, Chancellor, survived, but Adams died a month later.
Following Muhammad's testimony, jurors watched a videotaped deposition by forensic scientist Henry Lee, who cast doubts on the prosecution's argument that Carruth was present at the shooting.
Lee gave his testimony Dec. 6 after the jury was sent home.
Judge Charles Lamm agreed to a request by defence lawyer David Rudolf to allow Lee to testify out of turn to accommodate Lee's schedule.
Prosecution witnesses have said Carruth, driving in front of Adams, stopped his car so she would have to stop her car, allowing the gunman in a third car to fire at her.
Lee, whose previous work includes the O.J. Simpson trial, said that of the five shots that hit Adams' car, three were fired straight at the car from a 90-degree angle.
The last two were fired at an angle, suggesting possible movement by Adams's car, he said.
Lee's inspection of the cars found no damage to the front of Adams's BMW sports car.
Had Adams tried to drive away, he said, there likely would have been a collision if Carruth's vehicle was in front of hers.
By Paul Nowell