Valtteri suffered a difficult evening under the lights at the Yas Marina Circuit, starting off strong and holding onto second position.
However, in the closing stages he started to struggle and eventually dropped to fifth, before pitting for a second set of tyres.
His issues may have been down to a brake problem, but the team needs to properly investigate the situation.
"After the stop we saw some odd braking behaviour, it was on the rear right," Toto explained.
"We couldn't really see what it was, we just saw that the balance wasn't right.
"That's why we made the stop to change the wheel and from then on it was a bit better.
"Before actually making a comment on performance I'd rather see the data."