The forward was not able to complete their come from behind 2-1 win over Wolves on Sunday.
Isak, who had injury issues last term as well, had to come off at half time in this game.
Post-game, Howe responded: "Alex substitution was enforced. It was his eye.
"I did not see what the issue was but I knew he had to come off. I don't know if it is serious but I absolutely hope not."
On taking off Sean Longstaff and Joelinton, and later Tino Livramento, Howe added: "I just felt we needed a different energy in the team. It is reflected in the quality of players we have waiting to play.
"I want to give them long enough to influence the game. I did not want to cut their time to short that they could not impact the game as we needed them to.
"I was pleased with their attitude when entering the pitch. The ability of the players is never questioned but they made a positive impact for us."