Vydra, the Czech striker who scored 20 goals for Watford last season, played only seven minutes against Southampton and Clarke said he is looking forward to working with both players this week.
He told the club's official website: "I didn't include Diego in the squad at all on Saturday after he travelled with Uruguay and went to Japan.
"When he came in to the club he was a little bit behind us in his preparation.
"Vydra - I have to be honest - I haven't seen much of. He came in for his medical last week and then went away with the Czech Republic.
"I thought he looked quite lively when he came on and I know he's done a full pre-season with Udinese so I think Matej will pick up the pace quickly."
- Sports & Recreation