The England left-back has been ruled out for up to six weeks with a fractured toe suffered in the first half of in Saturday's Merseyside derby, which eventually forced him off in the 3-3 draw at Goodison Park.
However, Martinez believes the injury further underlined the defender's character as despite breaking a bone, Baines was determined to play on.
"Once more it shows you what an incredible character we have as he never wanted to stay in the dressing room, he wanted to help the team but in the end he had to come off," said the Spaniard.
"We have had the news there is a fracture in his phalange in the right foot.
"That is still a little bit up in the air as to how long he is going to be out.
"It could be up to six weeks but knowing Leighton it will probably be less than that. It is how he reacts to the treatment he is going to have.
"It is a real disappointment to lose Leighton for any space of days, never mind weeks."
Such has been the 28-year-old's permanence in the starting line-up over the last few years there is no ready-made, experienced replacement to step into the breach.
Gareth Barry filled in for Baines at left-back, a role he performed intermittently earlier in his career, but it is unlikely the 32-year-old will continue there in the interim such has been his impact in central midfield.
Martinez is looking for someone to come in and grasp the chance but knows it will be a challenge for his side to lose a player who has been the Premier League's best left-back for at least the last two years.
"Over the course of the season if you want to be a successful team you need to have those options and you need to have players ready to take opportunities," he told evertontv.
"You need to find out as a team how you cope with injuries and suspensions.
"In that respect we have plenty of options. It is an opportunity for someone to show they can help the team."
On the positive side centre-back Antolin Alcaraz played his first match after almost four months out with a hamstring injury.
The Paraguay international has yet to feature in the first team squad since following Martinez from Wigan in the summer but came through a run-out in a friendly.
Hibbert, fit again after a spell on the sidelines, and Stones were also involved in the game.
"We had a very good exercise on Monday, a friendly behind closed doors against Sheffield Wednesday," added the Toffees boss.
"Antolin played 45 minutes and showed no signs of not being fully fit, which is very pleasing.
"He has had a really difficult time and has been fighting strongly to help the team and I don't think it will be too long until we see Antolin available and in a position where he can help in this heavy period.
"We have 10 games in six weeks so we need everyone ready and available.
"It was great to see the likes of Antolin, Tony Hibbert and John Stones showing that they are desperate to play."
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- Tony Hibbert