Honduran Izaguirre suffered a head injury when denying Thistle wing-back Christie Elliott a shot at goal early in the second half of the Hoops' 2-1 victory at Firhill.
The defender was clearly feeling some discomfort but managed to play on until he was caught on the back of the head by team-mate Virgil Van Dyk during the celebrations for substitute Amido Balde's 75th-minute winner.
And Greece striker Samaras forced the visitors to play the final 10 minutes with just 10 men after he departed with blood pouring from a knee injury.
Speaking to Sky Sports, Celtic manager Lennon said: "Emilio took a knock to the head so that's very, very worrying.
"He can't remember going for the shot and we had to very quickly remind him of it.
"Another worry is Sammy. He has a four-inch gash across his knee which he is having some stitches put in now."
Of the game, which extended Celtic's unbeaten start to the season to 10, Lennon said: "It was a great win. We were sloppy at times with our finishing and should have been out of sight at half-time
"It was a difficult game under difficult conditions and circumstances. I felt we didn't start the second half particularly well, but our commitment was fantastic.
"I think Scott Fox made three great one-on-one saves and at 1-1 Partick Thistle were always in the game and they're a good team. Our reaction was good though and it was a brilliant win."