(Cover) - EN Showbiz - Ashton Kutcher thinks Natalie Portman is a modern great, who is so talented shes hard to act alongside.

The 33-year-old appears with Natalie in new movie No Strings Attached, about a pair who embark on a casual relationship. Ashton was blown away by Natalies acting ability, which he thinks dwarfs many of her contemporaries.

Shes probably one of the best actresses of my generation. I believe she is and theres a blessing and a curse in that as an actor, he told Cover Media.

He added it was sometimes difficult to match her performance and as a result he often put himself under intense pressure to shine.

Because... you know everything you get across from you is going to be real and honest and reactive and beautiful, at the same time when the light shines in the dark room all the dust shows and so it was a challenge for me to really to be as honest as she is.

Despite the stressful working conditions, Ashton has praised Natalie for her likeability. He believes the pair worked in harmony, which made for a comfortable pairing, despite Ashtons insecurities.

Its easier when you like the person and shes very likeable. I dont know that its something you can... manufacture. Ive generally found that you can have really good chemistry with someone that you can argue well with and I think Natalie and I both really appreciate being right and I think that that makes for good chemistry. I think Natalie could have chemistry with this cup is she wanted to, he added.

No Strings Attached is released in the UK on February 25. (C) Cover Media