Mauricio Pochettino fielded a strong side as Spurs saw off Fiorentina 3-0 on Thursday night and the Argentinian will be hoping his players recover in time to resume their title charge at home to Swansea on Sunday.
Tottenham's record following Europa League games this season has improved but there have still been slip-ups, with surprise defeats at home to Newcastle in December and Crystal Palace last weekend both coming after midweek ties.
Pochettino's commitment to the European campaign could hurt his team's chances of winning a first league title since 1961 but Dier is adamant tiredness will not be a factor.
"We haven't even thought about it to be honest, no-one has mentioned it really," Dier said.
"In the FA Cup and the Europa League we've managed to rotate a bit. Everyone has had a rest, everyone has got minutes under their belt, so as a squad we're in a very good position physically and mentally going into the final stage.
"Every game is huge now until the end of the season so we've got to be ready for it.
"The win against Fiorentina was the first big game heading into the end of the season and we've done well. Hopefully we can continue this way."
The two legs of the last 16 will be played on March 10 and March 17 in the middle of a testing period for Spurs, which includes league matches against West Ham, Arsenal, Liverpool and Manchester United.
The victory over Fiorentina was important, however, in regaining confidence and momentum after last weekend's FA Cup exit to Crystal Palace ended an eight-match unbeaten run for Pochettino's men.
"At the moment we believe we can beat anyone," Dier said.
"We play without fear and we go for it and we proved that again against Fiorentina.
"The only way to bounce back is to get a win straight away. That's a big team's mentality.
"When you lose, you bounce back immediately and we've managed to do that which is a good sign."
Source: PA