Ryan Phillippe's ex-girlfriend might be carrying his baby.

Model Alexis Knapp dated the 36-year-old actor on and off for several months until September last year and is reportedly claiming the baby she is now carrying is his.

A source close to the actress revealed she could be as far as seven months into the pregnancy, saying: "She's in the second trimester. She's not commenting on who the father is."

However, another source said: "She has been telling people he is the father.

"Ryan doesn't know if he is the dad. If he is, he will take full responsibility for the child."

The baby would be Ryan's third child as he already has daughter Ava, 11, and seven-year-old son Deacon with his ex-wife Reese Witherspoon.

Another source close to both Ryan and Alex said the pair were "serious" when they were together and is confident Ryan will support her if the child is his.

They told Usmagazine.com: "He and Alexis were actually together for a while ... It was pretty serious.

"He's a good guy. He loves being a dad and takes being a dad really seriously."

Recently the 'Lincoln Lawyer' star hinted that reports he is dating actress Amanda Seyfried are true.

He told Ellen Degeneres on her TV show: "I'm dating. Not nearly as voracious as the magazines like to make out, [but] I am dating."