Crystal Palace had a second bid of £14.3 million rejected, following an initial offer of £12.5 million.
Brighton are also reportedly considering entering the race for the Senegal international.
Tvrdik told media outlet Kudy Bezi Zajic: "If Liverpool and Chelsea, who were also interested in him, had come with an offer of around 17-18 million euros, I would have hesitated to approach it differently from the perspective of promoting the club or the player's interest.
"If Chelsea comes, we wouldn't keep anyone. Nothing will change, it's just not possible objectively. One has to admit that the Czech league and Slavia have some limits.
“Even PSG, when it comes to breaking the bank, won't keep their player and he'll go to Real. We're part of a football chain and we're not at the top of it."