Stanislas Wawrinka has suggested that Andy Murray's ATP World Tour Finals performances may be affected by his upcoming Davis Cup showdown.

The Scotsman was beaten heavily by Rafael Nadal in his second match of the tournament at London's O2 Arena, requiring him to defeat Wawrinka on Friday to keep his hopes of progression alive.

Ahead of their meeting in London, the Swiss - who helped his nation win the Davis Cup last year - believes that Murray's focus may be elsewhere at this moment in time.

Speaking to The Mirror, he said: "It's tough to say what Murray's thinking - if he's completely focused or not. If he's already thinking too much about the Davis Cup. It's impossible to know exactly what we can expect from him.

"For sure if I look at his match against Rafa, I think he was a little bit flat. The fact he practised so much after Paris on clay to get the rhythm doesn't help him to feel completely fresh this week.

"We'll see. Maybe he's going to feel more relaxed or maybe he's not going to be completely here. If he's mentally not really here, then he's a different player."

Wawrinka came out on top the last time he met Murray in the 2013 US Open, claiming a straight-sets win.