Paul Lambert's side leaked goals during a miserable January when they were dumped out of both cup competitions by lower league opposition and fell into a serious relegation battle.
Clark has taken on a senior role in the continued absence of Richard Dunne and the 23-year-old has come in for some criticism. However, Tardelli feels that is unfair on the youngster.
"I think Ciaran is playing very well," said the Irish assistant. "It's true that Aston Villa concede many goals but a player can change in the national team. Now, in this moment, Ciaran Clark is the best player in Aston Villa because they believe in him."
Clark has a strong chance of featuring in the friendly with Poland if he overcomes a knock on the knee that forced him to sit out training yesterday.
The composition of the defence is the main dilemma that faces the management team heading into this encounter.
Tardelli confirmed that John O'Shea will kick off the game at centre-half, with Paul McShane deputising for Coleman at right-full. Greg Cunningham is in line for a start at left-full ahead of Stephen Ward, although Trapattoni is mulling over his options in that department.
"Keogh is a good player," said Tardelli. "He is like St Ledger, maybe stronger physically, and the head is like Richard Dunne. It's possible that in the future he can play for us."
"We have many players. After the match we will know if we have good options or not."
Trapattoni suggested that he would like to give Wes Hoolahan another chance in this match, possibly in a floating role behind lone striker Conor Sammon. While the assistant agreed it might be on the cards at some stage, he suggested that Hoolahan might be more likely to feature in the second half of a game where a number of players will be given just 45 minutes to keep their clubs happy.
Shane Long, who was in action on Sunday, also sat out Monday's proceedings and Tardelli gave the impression that his fitness will have a major impact on the initial selection. Jonathan Walters, Kevin Doyle, Simon Cox and Andy Keogh are also competing for a forward berth. Trapattoni is likely to name his starting side this afternoon.