Midfielder Kroos, 24, joined the La Liga side from Bayern Munich for a fee reported to be 25 million euros ($33.82 million) just days after playing an integral role in Germany's World Cup triumph.
The Columbian Rodriguez, 23, arrived from Monaco for a fee in the region of 80 million euros having won the Golden Boot as the tournament's top scorer with six goals in five matches.
"I watched James Rodriguez and Toni Kroos play in the World Cup and, for me, they were two of the best players in the competition," Modric told Marca. "They're great players and will only improve our team even more.
"Real Madrid have shown their ambition by bringing such fantastic signings to the club. It's great news for us, the players, because we always want to play with the best, and also for the supporters, who want to see the best players."
Los Blancos won the Champions League and King's Cup last season and Modric believes their stellar squad is capable of doing even better in the upcoming campaign.
"Every competition and every trophy is important at Real Madrid," the 28-year-old added. "It would be marvellous to be able to win all six (available trophies), but it will be very, very tough. We'll face some very good teams on the way.
"The pressure will be the same as it always is at Real Madrid. There won't be as much as there was for La Decima (their 10th European title), which was enormous.
"Now it'll be the logical pressure involved with being Real Madrid, because of the club's history and the fact that we're the current champions. It'll be easier after having won La Decima. I think it's our time."