Aston Villa manager Tim Sherwood has warned Ron Vlaar that he must prove his worth in the closing stages of the season to resolve the uncertainty surrounding his future.

Despite injuries preventing him from producing his best form on a regular basis since last summer's World Cup, Vlaar has been linked with a move to Manchester United when his contract expires at the end of the campaign.

Sherwood has admitted to not speaking to the Dutchman about a new deal, and has challenged the centre-back to impress over the next few weeks.

"You are always looking at what people are doing now rather than a few months ago," the Villa boss told reporters ahead of Saturday's meeting with United. "He will have far more options open to him if he is in the shop window that's for sure.

"He realises he needs to be playing. I haven't even bothered speaking to him. There's time for that when we are safe.

"He is just concentrating on getting fit to play. Without getting on the pitch, he's not going to be an attractive proposition to anybody."

Vlaar is expected to be available for selection for the first time since February when Villa travel to Old Trafford.